%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%
%W options.tex ACE documentation - options Alexander Hulpke
%W Joachim Neub"user
%W Greg Gamble
%%
%H $Id: options.tex,v 1.21 2006/01/26 16:15:05 gap Exp $
%%
%Y Copyright (C) 2000 Centre for Discrete Mathematics and Computing
%Y Department of Information Tech. & Electrical Eng.
%Y University of Queensland, Australia.
%%
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\Chapter{Options for ACE}
{\ACE} offers a wide range of options to direct and guide a coset
enumeration, most of which are available from {\GAP} through the
interface provided by the {\ACE} Package. We describe most of the
options available via the interface in this chapter; other options,
termed strategies, are defined in Chapter~"Strategy Options for ACE".
(Strategies are merely special options of {\ACE} that set a number of
options described in this chapter, all at once.) Yet other options,
for which interactive function alternatives are provided in
Chapter~"Functions for Using ACE Interactively", or which most {\GAP}
users are unlikely to need, are described in Appendix~"Other ACE
Options". From within a {\GAP} session, one may see the complete list
of {\ACE} options, after loading the {\ACE} Package (see
Section~"Loading the ACE Package"), by typing
\beginexample
gap> RecNames(KnownACEOptions);
[ "aceinfile", "aceignore", "aceignoreunknown", "acenowarnings", "aceecho",
"aceincomment", "aceexampleoptions", "silent", "lenlex", "semilenlex",
"incomplete", "sg", "rl", "aep", "ai", "ao", "aceoutfile", "asis", "begin",
"start", "bye", "exit", "qui", "cc", "cfactor", "ct", "check", "redo",
"compaction", "continu", "cycles", "dmode", "dsize", "default", "ds", "dr",
"dump", "easy", "echo", "enumeration", "felsch", "ffactor", "fill",
"group", "generators", "relators", "hard", "help", "hlt", "hole",
"lookahead", "loop", "max", "mendelsohn", "messages", "monitor", "mode",
"nc", "normal", "no", "options", "oo", "order", "path", "pmode", "psize",
"sr", "print", "purec", "purer", "rc", "recover", "contiguous", "rep",
"rfactor", "rt", "row", "sc", "stabilising", "sims", "standard",
"statistics", "stats", "style", "subgroup", "system", "text", "time", "tw",
"trace", "workspace" ]
\endexample
(See Section~"The KnownACEOptions Record".) Also, from within a {\GAP}
session, you may use {\GAP}'s help browser (see Chapter~"ref:The Help
System" in the {\GAP} Reference Manual); to find out about any
particular {\ACE} option, simply type: ```?option <option>''', where
<option> is one of the options listed above without any quotes, e.g.
\begintt
gap> ?option echo
\endtt
will display the section in this manual that describes the `echo'
option.
We begin this chapter with several sections discussing the nature of
the options provided. Please spend some time reading these sections.
To continue onto the next section on-line using {\GAP}'s help browser,
type:
\begintt
gap> ?>
\endtt
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\Section{Passing ACE Options}
Options are passed to the {\ACE} interface functions in either of the
two usual mechanisms provided by {\GAP}, namely:
\beginlist%unordered
\item{--} options may be set globally using the function `PushOptions'
(see Chapter~"ref:Options Stack" in the {\GAP} Reference Manual); or
\item{--} options may be appended to the argument list of any function
call, separated by a colon from the argument list (see "ref:Function
Calls" in the {\GAP} Reference Manual), in which case they are then
passed on recursively to any subsequent inner function call, which may
in turn have options of their own.
\endlist
In general, if {\ACE} is to be used interactively one should avoid
using the global method of passing options. In fact, it is recommended
that prior to calling `ACEStart' the `OptionsStack' be empty.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\Section{Warnings regarding Options}
As mentioned above, one can set options globally using the function
`PushOptions' (see Chapter~"ref:Options Stack" in the {\GAP} Reference
Manual); however, options pushed onto `OptionsStack', in this way,
remain there until an explicit `PopOptions()' call is made. In
contrast, options passed in the usual way behind a colon following a
function's arguments (see "ref:Function Calls" in the {\GAP} Reference
Manual) are local, and disappear from `OptionsStack' after the
function has executed successfully; nevertheless, a function, that is
passed options this way, will also see any global options or any
options passed down recursively from functions calling that function,
unless those options are over-ridden by options passed via the
function. Also note that duplication of option names for different
programs may lead to misinterpretations. Since a non-empty
`OptionsStack' is potentially a mine-field for the unwary user, the
function `ResetOptionsStack' (see~"ref:ResetOptionsStack" in the
Reference Manual) is now in the {\GAP} library and
\>FlushOptionsStack() F
introduced in version 3.001 of the {\ACE} Package to perform the same
function, is now a synonym for `ResetOptionsStack'; it simply executes
`PopOptions()' until `OptionsStack' is empty.
However, `ResetOptionsStack' (or `FlushOptionsStack') does not wipe
out the options already passed to an *interactive* {\ACE} process. We
have provided `GetACEOptions' (see~"GetACEOptions") to keep track of
options that the {\ACE} binary process still considers active, which
may or may not be still on the `OptionsStack'. There is the
interactive `SetACEOptions' (see~"SetACEOptions") to change such
options, or, of course, you can always elect to use `ACEQuit'
(see~"ACEQuit") and then start a new interactive {\ACE} process.
Finally, if `ACEIgnoreUnknownDefault := false'
(see~"ACEIgnoreUnknownDefault"), there will be situations where an
{\ACE} interface function needs to be told explicitly to ignore
options passed down recursively to it from calling functions. For this
purpose we have provided the options `aceignore' (see~"option
aceignore") and `aceignoreunknown' (see~"option aceignoreunknown").
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\Section{Abbreviations and mixed case for ACE Options}
Except for limitations imposed by {\GAP} e.g.\ clashes with {\GAP}
keywords and blank spaces not allowed in keywords, the options of the
{\ACE} interface are the same as for the binary; so, for example, the
options can appear in upper or lower case (or indeed, mixed case) and
most may be abbreviated. Below we only list the options in all lower
case, and in their longest form; where abbreviation is possible we
give the shortest abbreviation in the option's description e.g.~for
the `mendelsohn' option we state that its shortest abbreviation is
`mend', which means `mende', `mendel' etc., and indeed, `Mend' and
`MeND', are all valid abbreviations of that option. Some options have
synonyms e.g.~`cfactor' is an alternative for `ct'.
The complete list of {\ACE} options known to the {\ACE} interface
functions, their abbreviations and the values that they are known to
take may be gleaned from the `KnownACEOptions' record (see
Section~"The KnownACEOptions Record").
Options for the {\ACE} interface functions
`ACECosetTableFromGensAndRels', `ACECosetTable', `ACEStats' and
`ACEStart' (see Chapter~"Functions for Using ACE Interactively"),
comprise the few non-{\ACE}-binary options (`silent', `aceinfile',
`aceoutfile', `aceignore', `aceignoreunknown', `acenowarnings',
`aceincomment', `aceecho' and `echo') discussed in
Section "Non-ACE-binary Options", (almost) all single-word {\ACE}
binary options and `purer' and `purec'. The options `purer' and
`purec' give the {\ACE} binary options `pure r' and `pure c',
respectively; (they are the only multiple-word {\ACE} binary options
that do not have a single word alternative). The *only* single-word
{\ACE} binary options that are *not* available via the {\ACE}
interface are abbreviations that clash with {\GAP} keywords (e.g.~`fi'
for `fill', `rec' for `recover' and `continu' for `continue'). The
detail of this paragraph is probably of little importance to the
{\GAP} user; these comments have been included for the user who wishes
to reconcile the respective functionalities of the {\ACE} interface
and the {\ACE} standalone, and are probably of most value to
standalone users.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\Section{Honouring of the order in which ACE Options are passed}
It is important to realize that {\ACE}'s options (even the
non-strategy options) are not orthogonal, i.e.\ the order in which
they are put to {\ACE} can be important. For this reason, except for a
few options that have no effect on the course of an enumeration, the
order in which options are passed to the {\ACE} interface is preserved
when those same options are passed to the {\ACE} binary. One of the
reasons for the non-orthogonality of options is to protect the user
from obtaining invalid enumerations from bad combinations of options;
another reason is that commonly one may specify a strategy option and
override some of that strategy's defaults; the general rule is that
the later option prevails. By the way, it's not illegal to select more
than one strategy, but it's not sensible; as just mentioned, the later
one prevails.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\Section{What happens if no ACE Strategy Option or if no ACE Option is passed}
If an {\ACE} interface function (`ACECosetTableFromGensAndRels',
`ACEStats', `ACECosetTable' or `ACEStart') is given no strategy
option, the `default' strategy (see Chapter~"Strategy Options for
ACE") is selected, and a number of options that {\ACE} needs to have a
value for are given default values, *prior* to the execution of any
user options, if any. This ensures that {\ACE} has a value for all its
``run parameters''; three of these are defined from the {\ACE}
interface function arguments; and the remaining ``run parameters'', we
denote by ``{\ACE} Parameter Options''. For user convenience, we have
provided the `ACEParameterOptions' record (see~"ACEParameterOptions"),
the fields of which are the ``{\ACE} Parameter Options''. The value of
each field (option) of the `ACEParameterOptions' record is either a
default value or (in the case of an option that is set by a strategy)
a record of default values that {\ACE} assumes when the user does not
define a value for the option (either indirectly by selecting a
strategy option or directly).
If the `default' strategy does not suffice, most usually a user will
select one of the other strategies from among the ones listed in
Chapter~"Strategy Options for ACE", and possibly modify some of the
options by selecting from the options in this chapter. It's not
illegal to select more than one strategy, but it's not sensible; as
mentioned above, the later one prevails.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\Section{Interpretation of ACE Options}
Options may be given a value by an assignment to the name (such as
`time := <val>'); or be passed without assigning a value, in which
case {\GAP} treats the option as *boolean* and sets the option to the
value `true', which is then interpreted by the {\ACE} interface
functions. Technically speaking the {\ACE} binary itself does not have
boolean options, though it does have some options which are declared
by passing without a value (e.g. the `hard' strategy option) and
others that are boolean in the C-sense (taking on just the values 0 or
1). The behaviour of the {\ACE} interface functions
(`ACECosetTableFromGensAndRels', `ACEStats', `ACECosetTable' or
`ACEStart') is essentially to restore as much as is possible a
behaviour that mimics the {\ACE} standalone; a `false' value is always
translated to 0 and `true' may be translated to any of no-value, 0 or
1. Any option passed with an assigned value <val> other than `false'
or `true' is passed with the value <val> to the {\ACE} binary. Since
this may appear confusing, let's consider some examples.
\beginlist%unordered
\item{--} The `hard' strategy option (see~"option hard") should be
passed without a value, which in turn is passed to the {\ACE} binary
without a value. However, the {\ACE} interface function cannot
distinguish the option `hard' being passed without a value, from it
being passed via `hard := true'. Passing `hard := false' or `hard :=
<val>' for any non-`true' <val> will however produce a warning message
(unless the option `acenowarnings' is passed) that the value 0 (for
`false') or <val> is unknown for that option. Nevertheless, despite
the warning, in this event, the {\ACE} interface function passes the
value to the {\ACE} binary. When the {\ACE} binary sees a line that it
doesn't understand it prints a warning and simply ignores it. (So
passing `hard := false' will produce warnings, but will have no ill
effects.) The reason we still pass *unknown* values to the {\ACE}
binary is that it's conceivable a future version of the {\ACE} binary
might have several `hard' strategies, in which case the {\ACE}
interface function will still complain (until it's made aware of the
new possible values) but it will perform in the correct manner if a
value expected by the {\ACE} binary is passed.
\item{--} The `felsch' strategy option (see~"option felsch") may be
passed without a value (which chooses the *felsch 0* strategy) or with
the values 0 or 1. Despite the fact that {\GAP} sees this option as
*boolean*; it is *not*. There are two Felsch strategies: *felsch 0*
and *felsch 1*. To get the *felsch 1* strategy, the user must pass
`felsch := 1'. If the user were to pass `felsch := false' the result
would be the *felsch 0* strategy (since `false' is always translated
to 0), i.e.~the same as how `felsch := true' would be interpreted. We
could protect the user more from such ideosyncrasies, but we have
erred on the side of simplicity in order to make the interface less
vulnerable to upgrades of the {\ACE} binary.
\endlist
The lesson from the two examples is: *check the documentation for an
option to see how it will be interpreted*. In general, options
documented (in this chapter) as *only* being no-value options can be
safely thought of as boolean (i.e.~you will get what you expect by
assigning `true' or `false'), whereas strategy (no-value) options
should *not* be thought of as boolean (a `false' assignment will *not*
give you what you might have expected).
Options that are unknown to the {\ACE} interface functions and not
ignored (see below), that are passed without a value, are *always*
passed to the {\ACE} binary as no-value options (except when the
options are ignored); the user can over-ride this behaviour simply by
assigning the intended value. Note that it is perfectly safe to allow
the {\ACE} binary to be passed unknown options, since {\ACE} simply
ignores options it doesn't understand, issues an error message (which
is just a warning and is output by {\GAP} unless `acenowarnings' (see
"option acenowarnings") is passed) and continues on with any other
options passed in exactly the way it would have if the ``unknown''
options had not been passed.
An option is ignored if it is unknown to the {\ACE} interface
functions and one of the following is true:
\beginlist%unordered
\item{--} the global variable `ACEIgnoreUnknownDefault' is set to
`false' (see~"ACEIgnoreUnknownDefault") or,
\item{--} the `aceignoreunknown' option (see~"option aceignoreunknown")
is passed, or
\item{--} the `aceignore' option is passed and the option is an
element of the list value of `aceignore' (see~"option aceignore").
\endlist
\index{debugging}
\indextt{ACEIgnoreUnknownDefault!use as debugging tool}
It is actually *recommended* that the user set
`ACEIgnoreUnknownDefault' to `false', since this will allow the user
to see when {\ACE} functions have been passed options that are
``unknown'' to the {\ACE} package. In this way the user will be
informed about misspelt options, for example. So it's a good debugging
tool. Also, if the {\ACE} binary is updated with a version with new
options then these will not be known by the package (the {\GAP} part)
and it will be necessary to set `ACEIgnoreUnknownDefault' to `false'
in order for the new options to be passed to the binary. When an
{\ACE} function is invoked indirectly by some function that was called
with non-{\ACE} options the warning messages may begin to be annoying,
and it's then a simple matter to set `ACEIgnoreUnknownDefault' back to
the {\ACE} 3.003 default value of `true'.
Warning messages regarding unknown options are printed unless the
`acenowarnings' (see "option acenowarnings") is passed or the option
is ignored.
To see how options are interpreted by an {\ACE} interface function,
pass the `echo' option.
As mentioned above, any option that the {\ACE} binary doesn't
understand is simply ignored and a warning appears in the output from
{\ACE}. If this occurs, you may wish to check the input fed to {\ACE}
and the output from {\ACE}, which when {\ACE} is run non-interactively
are stored in files whose full path names are recorded in the record
fields `ACEData.infile' and `ACEData.outfile', respectively.
Alternatively, both interactively and non-interactively one can set
the `InfoLevel' of `InfoACE' to 3 (see~"SetInfoACELevel"), to see the
output from {\ACE}, or to 4 to also see the commands directed to
{\ACE}.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\Section{An Example of passing Options}
Continuing with the example of Section~"Using ACE Directly to Generate
a Coset Table", one could set the `echo' option to be true, use the
`hard' strategy option, increase the workspace to $10^7$ words and
turn messaging on (but to be fairly infrequent) by setting `messages'
to a large positive value as follows:
\begintt
gap> ACECosetTable(fgens, rels, [c]
> : echo, hard, Wo := 10^7, mess := 10000);;
\endtt
As mentioned in the previous section, `echo' may be thought of as a
boolean option, whereas `hard' is a strategy option (and hence should
be thought of as a no-value option). Also, observe that two options
have been abbreviated: `Wo' is a mixed case abbreviation of
`workspace', and `mess' is an abbreviation of `messages'.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\Section{The KnownACEOptions Record}
\>`KnownACEOptions' V
is a {\GAP} record whose fields are the {\ACE} options known to the
{\ACE} interface; each field (known {\ACE} option) is assigned to a
list of the form `[<i>, <ListOrFunction>]', where `<i>' is an integer
representing the length of the shortest abbreviation of the option and
`<ListOrFunction>' is either a list of (known) allowed values or a
boolean function that may be used to determine if the given value is a
(known) valid value e.g.
\beginexample
gap> KnownACEOptions.compaction;
[ 3, [ 0 .. 100 ] ]
\endexample
indicates that the option `compaction' may be abbreviated to `com'
and the (known) valid values are in the (integer) range 0 to 100; and
\beginexample
gap> KnownACEOptions.ct;
[ 2, <Operation "IS_INT"> ]
\endexample
indicates that there is essentially no abbreviation of `ct' (since its
shortest abbreviation is of length 2), and a value of `ct' is known
to be valid if `IsInt' returns true for that value.
For user convenience, we provide the function
\>ACEOptionData( <optname> ) F
which for a string <optname> representing an {\ACE} option (or a guess
of one) returns a record with the following fields:
\beginitems
\quad`name' & <optname> (unchanged);
\quad`known' & `true' if <optname> is a valid mixed case abbreviation
of a known {\ACE} option, and false otherwise;
\quad`fullname'& the lower case unabbreviated form of <optname> if the
`known' field is set `true', or <optname> in all lower case,
otherwise;
\quad`synonyms'& a list of known {\ACE} options synonymous with
<optname>, in lowercase unabbreviated form, if the `known' field is
set `true', or a list containing just <optname> in all lower case,
otherwise;
\quad`abbrev' & the shortest lowercase abbreviation of <optname> if
the `known' field is set `true', or <optname> in all lower case,
otherwise.
\enditems
For more on synonyms of {\ACE} options, see~"ACEOptionSynonyms".
The function `ACEOptionData' provides the user with all the query
facility she should ever need; nevertheless, we provide the following
functions.
\>IsKnownACEOption( <optname> ) F
returns `true' if <optname> is a mixed case abbreviation of a field of
`KnownACEOptions', or `false' otherwise.
`IsKnownACEOption(<optname>);' is equivalent to
\)\kernttindent{ACEOptionData(<optname>).known;}
\>ACEPreferredOptionName( <optname> ) F
returns the lowercase unabbreviated first alternative of <optname> if
it is a known {\ACE} option, or <optname> in lowercase, otherwise.
`ACEPreferredOptionName(<optname>);' is equivalent to
\)\kernttindent{ACEOptionData(<optname>).synonyms[1];}
\>IsACEParameterOption( <optname> ) F
returns true if <optname> is an ``{\ACE} parameter option''. ({\ACE}
Parameter Options are described in Section~"ACEParameterOptions").
`IsACEParameterOption(<optname>);' is equivalent to
\)\kernttindent{ACEPreferredOptionName(<optname>) in RecNames(ACEParameterOptions);}
\>IsACEStrategyOption( <optname> ) F
returns true if <optname> is an ``{\ACE} strategy option'' (see
Section~"The ACEStrategyOptions list").
`IsACEStrategyOption(<optname>);' is equivalent to
\)\kernttindent{ACEPreferredOptionName(<optname>) in ACEStrategyOptions;}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\Section{The ACEStrategyOptions List}
\>`ACEStrategyOptions' V
is a {\GAP} list that contains the strategy options known to the
{\ACE} interface functions:
\beginexample
gap> ACEStrategyOptions;
[ "default", "easy", "felsch", "hard", "hlt", "purec", "purer", "sims" ]
\endexample
See Chapter~"Strategy Options for ACE" for details regarding the
{\ACE} strategy options.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\Section{ACE Option Synonyms}\nolabel
\>`ACEOptionSynonyms' V
is a {\GAP} record. A number of known {\ACE} options have synonyms.
The fields of the `ACEOptionSynonyms' record are the ``preferred''
option names and the values assigned to the fields are the lists of
synonyms of those option names. What makes an option name
``preferred'' is somewhat arbitrary (in most cases, it is simply the
shortest of a list of synonyms). For a ``preferred'' option name
<optname> that has synonyms, the complete list of synonyms may be
obtained by concatenating `[ <optname> ]' and
`ACEOptionSynonyms.(<optname>)', e.g.
\beginexample
gap> Concatenation( [ "messages" ], ACEOptionSynonyms.("messages") );
[ "messages", "monitor" ]
\endexample
More generally, for an arbitrary option name <optname> its list of
synonyms (which may be a list of one element) may be obtained as the
`synonyms' field of the record returned by `ACEOptionData(<optname>)'
(see~"ACEOptionData").
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\Section{Non-ACE-binary Options}
\>`NonACEbinOptions' V
is a {\GAP} list of options that have meaning only for the {\ACE}
Package interface, i.e.~options in `KnownACEOptions' that are *not*
{\ACE} binary options; each such option is described in detail below.
*Except* for the options listed in `NonACEbinOptions' and those
options that are excluded via the `aceignore' and `aceignoreunknown'
options (described below), *all* options that are on the
`OptionsStack' when an {\ACE} interface function is called, are passed
to the {\ACE} binary. Even options that produce the warning message:
```unknown (maybe new) or bad''', by virtue of not being a field of
`KnownACEOptions', are passed to the {\ACE} binary (except that the
options `purer' and `purec' are first translated to `pure r' and `pure
c', respectively). When the {\ACE} binary encounters an option that it
doesn't understand it issues a warning and simply ignores it; so
options accidentally passed to {\ACE} are unlikely to pose problems.
We also mention here, since it is related to an option of this
section, the following.
\>`ACEIgnoreUnknownDefault' V
is a global variable (*not* an option) that is initially set by the
{\ACE} package to `true', and is the default action that {\ACE} takes
for options that are unknown to the {\ACE} package (but may be new
options provided in a new version of the {\ACE} binary). Despite the
fact that it is normally set `true', it is recommended (especially for
the novice user of the {\ACE} package) to set `ACEIgnoreUnknownDefault
:= false'; the worst that can happen is being annoyed by a profusion
of warnings of unknown options. For individual functions, the user may
use the option `aceignoreunknown' (see~"option aceignoreunknown") to
over-ride the setting of `ACEIgnoreUnknownDefault'.
Here now, are the few options that are available to the {\GAP}
interface to {\ACE} that have no counterpart in the {\ACE} standalone:
\beginitems
\>`silent'{option silent}@{option `silent'}&
Inhibits an `Error' return when generating a coset table.
If a coset enumeration that invokes `ACECosetTableFromGensAndRels'
does not finish within the preset limits, an error is raised by the
interface to {\GAP}, unless the option `silent' or `incomplete'
(see~"option incomplete") has been set; in the former case, `fail' is
returned. This option is included to make the behaviour of
`ACECosetTableFromGensAndRels' compatible with that of the function
`CosetTableFromGensAndRels' it replaces. If the option `incomplete' is
also set, it overrides option `silent'.
\>`lenlex'{option lenlex}@{option `lenlex'}&
Ensures that `ACECosetTable' and `ACECosetTableFromGensAndRels' output
a coset table that is `lenlex' standardised.
The `lenlex' scheme, numbers cosets in such a way that their
``preferred'' (coset) representatives, in an alphabet consisting of
the user-submitted generators and their inverses, are ordered first
according to `length' and then according to a `lexical' ordering. In
order to describe what the `lenlex' scheme's `lexical' ordering is,
let us consider an example. Suppose the generators submitted by the
user are, in user-supplied order, `[x, y, a, b]', and represent the
inverses of these generators by the corresponding uppercase letters:
`[X, Y, A, B]', then the `lexical' ordering of `lenlex' is that
derived from defining `x \< X \< y \< Y \< a \< A \< b \< B'.
*Notes:*
In some circumstances, {\ACE} prefers to swap the first two
generators; such cases are detected by the function
`IsACEGeneratorsInPreferredOrder' (see
"IsACEGeneratorsInPreferredOrder"). In such cases, special action is
taken to avoid {\ACE} swapping the first two generators; this action
is described in the notes for `ACEStandardCosetNumbering'
(see~"ACEStandardCosetNumbering"). When this special action is
invoked, a side-effect is that any setting of the `asis' (see~"option
asis") option by the user is ignored.
The `lenlex' standardisation scheme is the default coset table
standardisation scheme of {\GAP} (since version 4.3). However,
`semilenlex' was the standardisation scheme for versions of {\GAP} up
to {\GAP}~4.2. Both schemes are described in detail in Section~"Coset
Table Standardisation Schemes".
\>`semilenlex'{option semilenlex}@{option `semilenlex'}&
Ensures that `ACECosetTable' and `ACECosetTableFromGensAndRels' output
a coset table that is `semilenlex' standardised.
The `semilenlex' scheme, numbers cosets in such a way that their
``preferred'' (coset) representatives, in an alphabet consisting of
only the user-submitted generators, are ordered first according to
`length' and then according to a `lexical' ordering.
*Note:*
Up to {\GAP}~4.2, `semilenlex' was the default standardisation scheme
used by {\GAP} (see also~"option lenlex").
\>`incomplete'{option incomplete}@{option `incomplete'}&
Allows the return of an `incomplete' coset table, when a coset
enumeration does not finish within preset limits.
If a coset enumeration that invokes `ACECosetTableFromGensAndRels' or
`ACECosetTable' does not finish within the preset limits, an error is
raised by the interface to {\GAP}, unless the option `silent'
(see~"option silent") or `incomplete' has been set; in the latter
case, a partial coset table, that is a valid {\GAP} list of lists, is
returned. Each position of the table without a valid coset number
entry is filled with a zero. If the option `silent' is also set,
`incomplete' prevails. Since {\GAP}~4.3, an incomplete table is
returned reduced (i.e.~with insignificant coset numbers --- those
appearing only in their place of definition --- removed) and `lenlex'
standardised (regardless of whether the `semilenlex' option is in
force). (For GAP~4.2, an incomplete table was returned unstandardised
unless the `lenlex' option (see~"option lenlex") was also set, and the
table was also not reduced.) When an incomplete table is returned, a
warning is emitted at `InfoACE' or `InfoWarning' level 1.
\>`aceinfile:=<filename>'{option aceinfile}@{option `aceinfile'}&
Creates an {\ACE} input file <filename> for use with the standalone
only; <filename> should be a string. (Shortest abbreviation: `acein'.)
This option is only relevant to `ACECosetTableFromGensAndRels' and is
ignored if included as an option for invocations of `ACEStats' and
`ACEStart'. If this option is used, {\GAP} creates an input file with
filename <filename> only, and then exits (i.e.~the {\ACE} binary is
not called). This option is provided for users who wish to work
directly with the {\ACE} standalone. The full path to the input file
normally used by {\ACE} (i.e.~when option `aceinfile' is not used) is
stored in `ACEData.infile'.
\>`aceoutfile:=<filename>'{option aceoutfile}@{option `aceoutfile'}&
Redirects {\ACE} output to file <filename>; <filename> should be a
string. (Shortest abbreviation: `aceo'.)
This is actually a synonym for the `ao' option. Please refer
to~"option ao", for further discussion of this option.
\>`aceignore:=<optionList>'{option aceignore}@{option `aceignore'}&
Directs an {\ACE} function to ignore the options in <optionList>;
<optionList> should be a list of strings.
(Shortest abbreviation: `aceig'.)
If a function called with its own options, in turn calls an {\ACE}
function for which those options are not intended, the {\ACE} function
will pass those options to the {\ACE} binary. If those options are
unknown to the {\ACE} interface (and `ACEIgnoreUnknownDefault :=
false' and `aceignoreunknown' is not passed;
see~"ACEIgnoreUnknownDefault" and~"option aceignoreunknown") a warning
is issued. Options that are unknown to the {\ACE} binary are simply
ignored by {\ACE} (and a warning that the option was ignored appears
in the {\ACE} output, which the user will not see unless the
`InfoLevel' of `InfoACE' or `InfoWarning' is set to 1). This option
enables the user to avoid such options being passed at all, thus
avoiding the warning messages and also any options that coincidentally
are {\ACE} options but are not intended for the {\ACE} function being
called.
\>`aceignoreunknown'{option aceignoreunknown}@{option `aceignoreunknown'}&
Directs an {\ACE} function to ignore any options not known to the
{\ACE} interface.
(Shortest abbreviation: `aceignoreu'.)
This option is provided for similar reasons to `aceignore'. Normally,
it is safe to include it, to avoid aberrant warning messages from the
{\ACE} interface. However, fairly obviously, it should not be passed
without a value (or set to `true') in the situation where a new {\ACE}
binary has been installed with new options that are not listed among
the fields of `KnownACEOptions', which you intend to use. Omitting the
`aceignoreunknown' option is equivalent to setting it to the value of
`ACEIgnoreUnknownDefault' (see "ACEIgnoreUnknownDefault"); i.e.~it is
superfluous if `ACEIgnoreUnknownDefault := true' unless
`aceignoreunknown' is set to `false'.
\>`acenowarnings'{option acenowarnings}@{option `acenowarnings'}&
Inhibits the warning message ```unknown (maybe new) or bad option'''
for options not listed in `KnownACEOptions'.
(Shortest abbreviation: `acenow'.)
This option suppresses the warning messages for unknown options (to
the {\ACE} interface), but unlike `aceignore' and `aceignoreunknown'
still allows them to be passed to the {\ACE} binary.
\>`echo'{option echo}@{option `echo'}
\>`echo:=2'{option echo}@{option `echo'}&
Echoes arguments and options (and indicates how options were handled).
Unlike the previous options of this section, there *is* an {\ACE}
binary option `echo'. However, the `echo' option is handled by the
{\ACE} interface and is not passed to the {\ACE} binary. (If you wish
to put `echo' in a standalone script use the `aceecho' option
following.) If `echo' is passed with the value 2 then a list of the
options (together with their values) that are set via {\ACE} defaults
are also echoed to the screen.
\>`aceecho'{option aceecho}@{option `aceecho'}&
The {\ACE} binary's `echo' command.
This option is only included so that a user *can* put an `echo'
statement in an {\ACE} standalone script. Otherwise, use `echo'
(above).
\>`aceincomment:=<string>'{option aceincomment}@{option `aceincomment'}&
Print comment <string> in the {\ACE} input; <string> must be a string.
(Shortest abbreviation: `aceinc'.)
This option prints the comment <string> behind a sharp sign (`\#') in
the input to {\ACE}. Only useful for adding comments (that {\ACE}
ignores) to standalone input files.
\>`aceexampleoptions'{option aceexampleoptions}@{option `aceexampleoptions'}&
An *internal* option for `ACEExample'.
This option is passed *internally* by `ACEExample' to the {\ACE}
interface function it calls, when one invokes `ACEExample' with
options. Its purpose is to provide a mechanism for the over-riding of
an example's options by the user. The option name is deliberately long
and has no abbreviation to discourage user use.
\enditems
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\Section{ACE Parameter Options}\nolabel
\>`ACEParameterOptions' V
is a {\GAP} record, whose fields are the ``{\ACE} Parameter Options''.
The ``{\ACE} Parameter Options'' are options which, if not supplied a
value by the user, are supplied a default value by {\ACE}. In fact,
the ``{\ACE} Parameter Options'' are those options that appear (along
with `Group Generators', `Group Relators' and `Subgroup Generators',
which are defined from {\ACE} interface function arguments) in the
``Run Parameters'' block of {\ACE} output, when, for example, the
`messages' option is non-zero.
For each field ({\ACE} parameter option) of the `ACEParameterOptions'
record, the value assigned is the default value (or a record of
default values) that are supplied by {\ACE} when the option is not
given a value by the user (either indirectly by selecting a strategy
option or directly).
In the cases where the value of a field of the `ACEParameterOptions'
record is itself a record, the fields of that record are `default' and
strategies for which the value assigned by that strategy differs from
the `default' strategy. A ``strategy'', here, is the strategy option
itself, if it is only a no-value option, or the strategy option
concatenated with any of its integer values (as strings), otherwise
(e.g.~`felsch0' and `sims9' are strategies, and `hlt' is both a
strategy and a strategy option). As an exercise, the reader might like
to try to reproduce the table at the beginning of Chapter~"Strategy
Options for ACE" using the `ACEParameterOptions' record. (Hint: you
first need to select those fields of the `ACEParameterOptions' record
whose values are records with at least two fields.)
*Note:*
Where an ``{\ACE} Parameter Option'' has synonyms, only the
``preferred'' option name (see~"ACEOptionSynonyms") appears as a field
of `ACEParameterOptions'. The complete list of ``{\ACE} Parameter
Options'' may be obtained by
\beginexample
gap> Concatenation( List(RecNames(ACEParameterOptions),
> optname -> ACEOptionData(optname).synonyms) );
[ "asis", "ct", "cfactor", "compaction", "dmode", "dsize", "enumeration",
"fill", "ffactor", "hole", "lookahead", "loop", "max", "mendelsohn",
"messages", "monitor", "no", "path", "pmode", "psize", "rt", "rfactor",
"row", "subgroup", "time", "workspace" ]
\endexample
We describe the ``{\ACE} Parameter Options'' in the Sections~"General
ACE Parameter Options that Modify the Enumeration Process", "ACE
Parameter Options Modifying C Style Definitions", "ACE Parameter
Options for R Style Definitions", "ACE Parameter Options for Deduction
Handling", "Technical ACE Parameter Options", "ACE Parameter Options
controlling ACE Output", and~"ACE Parameter Options that give Names to
the Group and Subgroup", following.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\Section{General ACE Parameter Options that Modify the Enumeration Process}
\beginitems
\>`asis'{option asis}@{option `asis'}&
Do not reduce relators. (Shortest abbreviation: `as'.)
By default, {\ACE} freely and cyclically reduces the relators, freely
reduces the subgroup generators, and sorts relators and subgroup
generators in length-increasing order. If you do not want this, you
can switch it off by setting the `asis' option.
*Notes:* As well as allowing you to use the presentation *as* it *is*
given, this is useful for forcing definitions to be made in a
prespecified order, by introducing dummy (i.e., freely trivial)
subgroup generators. (Note that the exact form of the presentation
can have a significant impact on the enumeration statistics.) For
some fine points of the influence of `asis' being set on the treatment
of involutory generators see the {\ACE} standalone manual.
\>`ct:=<val>'{option ct}@{option `ct'}
\>`cfactor:=<val>'{option cfactor}@{option `cfactor'}&
Number of C style definitions per pass; `<val>' should be an integer.
(Shortest abbreviation of `cfactor' is `c'.)
The absolute value of `<val>' sets the number of C style definitions
per pass through the enumerator's main loop. The sign of `<val>' sets
the style. The possible combinations of the values of `ct' and `rt'
(described below) are given in the table of enumeration styles in
Section~"Enumeration Style".
\>`rt:=<val>'{option rt}@{option `rt'}
\>`rfactor:=<val>'{option rfactor}@{option `rfactor'}&
Number of R style definitions per pass; `<val>' should be an integer.
(Shortest abbreviation of `rfactor' is `r'.)
The absolute value of `<val>' sets the number of R style definitions
per pass through the enumerator's main loop. The sign of `<val>' sets
the style. The possible combinations of the values of `ct' (described
above) and `rt' are given in the table of enumeration styles in
Section~"Enumeration Style".
\>`no:=<val>'{option no}@{option `no'}&
The number of group relators to include in the subgroup;
`<val>' should be an integer greater than or equal to $-1$.
It is sometimes helpful to include the group relators into the list of
the subgroup generators, in the sense that they are applied to coset
number 1 at the start of an enumeration. A value of 0 for this option
turns this feature off and the (default) argument of $-1$ includes all
the relators. A positive argument includes the specified number of
relators, in order. The `no' option affects only the C style
procedures.
\>`mendelsohn'{option mendelsohn}@{option `mendelsohn'}&
Turns on mendelsohn processing. (Shortest abbreviation: `mend'.)
Mendelsohn style processing during relator scanning/closing is turned
on by giving this option. Off is the default, and here relators are
scanned only from the start (and end) of a relator. Mendelsohn ``on''
means that all (different) cyclic permutations of a relator are
scanned.
The effect of Mendelsohn style processing is case-specific. It can
mean the difference between success or failure, or it can impact the
number of coset numbers required, or it can have no effect on an
enumeration's statistics.
*Note:* Processing all cyclic permutations of the relators can be very
time-consuming, especially if the presentation is large. So, all
other things being equal, the Mendelsohn flag should normally be left
off.
\enditems
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\Section{ACE Parameter Options Modifying C Style Definitions}
\atindex{C style}{@C style!definition}
The next three options are relevant only for making *C style
definitions* (see Section~"Enumeration Style"). Making definitions in
C style, that is filling the coset table line by line, it can be very
advantageous to switch to making definitions from the preferred
definition stack. Possible definitions can be extracted from this
stack in various ways and the two options `pmode' and `psize'
(see~"option pmode" and~"option psize" respectively) regulate this.
However it should be clearly understood that making all definitions
from a preferred definition stack one may violate the condition of
Mendelsohn's theorem, and the option `fill' (see~"option fill") can be
used to avoid this.
\beginitems
\>`fill:=<val>'{option fill}@{option `fill'}
\>`ffactor:=<val>'{option ffactor}@{option `ffactor'}&
Controls the preferred definition strategy by setting the fill factor;
`<val>' must be a non-negative integer.
(Shortest abbreviation of `fill' is `fil', and shortest abbreviation
of `ffactor' is `f'.)
Unless prevented by the fill factor, gaps of length one found during
deduction testing are preferentially filled (see~\cite{Hav91}).
However, this potentially violates the formal requirement that all
rows in the coset table are eventually filled (and tested against the
relators). The fill factor is used to ensure that some constant
proportion of the coset table is always kept filled. Before defining a
coset number to fill a gap of length one, the enumerator checks
whether `fill' times the completed part of the table is at least the
total size of the table and, if not, fills coset table rows in
standard order (i.e.~C style; see Section~"Enumeration Style") instead
of filling gaps.
An argument of 0 selects the default value of $\lfloor 5(n+2)/4
\rfloor$, where $n$ is the number of columns in the table. This
default fill factor allows a moderate amount of gap-filling. If
`fill' is 1, then there is no gap-filling. A large value of `fill'
can cause what is in effect infinite looping (resolved by the coset
enumeration failing). However, in general, a large value does work
well. The effects of the various gap-filling strategies vary widely.
It is not clear which values are good general defaults or, indeed,
whether any strategy is always ``not too bad''.
This option is identified as `Fi' in the ``Run Parameters'' block
(obtained when `messages' is non-zero) of the {\ACE} output, since for
the {\ACE} binary, `fi' is an allowed abbreviation of `fill'. However,
`fi' is a {\GAP} keyword and so the shortest abbreviation of `fill'
allowed by the interface functions is `fil'.
\>`pmode:=<val>'{option pmode}@{option `pmode'}&
Option for preferred definitions; `<val>' should be in the integer
range 0 to 3. (Shortest abbreviation: `pmod'.)
The value of the `pmode' option determines which definitions are
preferred. If the argument is 0, then Felsch style definitions are
made using the next empty table slot. If the argument is non-zero,
then gaps of length one found during relator scans in Felsch style are
preferentially filled (subject to the value of `fill'). If the
argument is 1, they are filled immediately, and if it is 2, the
consequent deduction is also made immediately (of course, these are
also put on the deduction stack). If the argument is 3, then the gaps
of length one are noted in the preferred definition queue.
Provided such a gap survives (and no coincidence occurs, which causes
the queue to be discarded) the next coset number will be defined to
fill the oldest gap of length one. The default value is either 0 or 3,
depending on the strategy selected (see Chapter~"Strategy Options for
ACE"). If you want to know more details, read the code.
\>`psize:=<val>'{option psize}@{option `psize'}&
Size of preferred definition queue; `<val>' *must* be 0 or $2^n$, for
some integer $n>0$. (Shortest abbreviation: `psiz'.)
The preferred definition queue is implemented as a ring, dropping
earliest entries. An argument of 0 selects the default size of $256$.
Each queue slot takes two words (i.e., 8 bytes), and the queue can
store up to $2^n-1$ entries.
\enditems
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\Section{ACE Parameter Options for R Style Definitions}
\atindex{R style}{@R style!definition}
\beginitems
\>`row:=<val>'{option row}@{option `row'}&
Set the ``row filling'' option; `<val>' is either 0 or 1.
By default, ``row filling'' is on (i.e.~`true' or 1). To turn it off
set `row' to `false' or 0 (both are translated to 0 when passed to the
{\ACE} binary). When making HLT style (i.e.~R style; see
Section~"Enumeration Style") definitions, rows of the coset table are
scanned for holes after its coset number has been applied to all
relators, and definitions are made to fill any holes encountered. This
will, in particular, guarantee fulfilment of the condition of
Mendelsohn's Theorem. Failure to do so can cause even simple
enumerations to overflow.
\>`lookahead:=<val>'{option lookahead}@{option `lookahead'}&
Lookahead; `<val>' should be in the integer range 0 to 4.
(Shortest abbreviation: `look'.)
Although HLT style strategies are fast, they are local, in the sense
that the implications of any definitions/deductions made while
applying coset numbers may not become apparent until much later. One
way to alleviate this problem is to perform lookaheads occasionally;
that is, to test the information in the table, looking for deductions
or concidences. {\ACE} can perform a lookahead when the table
overflows, before the compaction routine is called. Lookahead can be
done using the entire table or only that part of the table above the
current coset number, and it can be done R style (scanning coset
numbers from the beginning of relators) or C style (testing all
definitions in all essentially different positions).
The following are the effects of the possible values of `lookahead':
\beginlist%unordered
\item{--} 0 disables lookahead;
\item{--} 1 does a partial table lookahead, R style;
\item{--} 2 does a whole table lookahead, C style;
\item{--} 3 does a whole table lookahead, R style; and
\item{--} 4 does a partial table lookahead, C style.
\endlist
The default is 1 if the `hlt' strategy is used and 0 otherwise; see
Chapter~"Strategy Options for ACE".
Section~"Enumeration Style" describes the various enumeration styles,
and, in particular, R style and C style.
\enditems
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\Section{ACE Parameter Options for Deduction Handling}
\beginitems
\>`dmode:=<val>'{option dmode}@{option `dmode'}&
Deduction mode; `<val>' should be in the integer range 0 to 4.
(Shortest abbreviation: `dmod'.)
A completed table is only valid if every table entry has been tested
in all essentially different positions in all relators. This testing
can either be done directly (`felsch' strategy; see~"option felsch")
or via relator scanning (`hlt' strategy; see~"option hlt"). If it is
done directly, then more than one deduction (i.e., table entry) can be
waiting to be processed at any one time. So the untested deductions
are stored in a stack. Normally this stack is fairly small but, during
a collapse, it can become very large.
This command allows the user to specify how deductions should be
handled. The value <val> has the following interpretations:
\beginlist%unordered
\item{--} $0$:
discard deductions if there is no stack space left;
\item{--} $1$:
as for $0$, but purge any redundant coset numbers on the top of the
stack at every coincidence;
\item{--} $2$:
as for 0, but purge all redundant coset numbers from the stack at
every coincidence;
\item{--} $3$:
discard the entire stack if it overflows; and
\item{--} $4$:
if the stack overflows, double the stack size and purge all redundant
coset numbers from the stack.
\endlist
The default deduction mode is either $0$ or $4$, depending on the
strategy selected (see Chapter~"Strategy Options for ACE"), and it is
recommended that you stay with the default. If you want to know more
details, read the well-commented C code.
*Notes:*
If deductions are discarded for any reason, then a final relator check
phase will be run automatically at the end of the enumeration, if
necessary, to check the result.
\>`dsize:=<val>'{option dsize}@{option `dsize'}&
Deduction stack size; `<val>' should be a non-negative integer.
(Shortest abbreviation: `dsiz'.)
Sets the size of the (initial) allocation for the deduction stack.
The size is in terms of the number of deductions, with one deduction
taking two words (i.e., 8 bytes). The default size, of $1000$, can be
selected by a value of 0. See the `dmode' entry for a (brief)
discussion of deduction handling.
\enditems
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\Section{Technical ACE Parameter Options}
The following options do not affect how the coset enumeration is done,
but how it uses the computer's resources. They might thus affect the
runtime as well as the range of problems that can be tackled on a
given machine.
\beginitems
\>`workspace:=<val>'{option workspace}@{option `workspace'}&
Workspace size in words (default $10^6$);
`<val>' should be an expression that evaluates to a positive integer,
or a string of digits ending in a `k', `M' or `G' representing a
multiplication factor of $10^3$, $10^6$ or $10^9$, respectively
e.g.~both `workspace := 2 * 10^6' and `workspace := "2M"' specify a
workspace of $2\times10^6$ words. Actually, if the value of
`workspace' is entered as a string, each of `k', `M' or `G' will be
accepted in either upper or lower case. (Shortest abbreviation: `wo'.)
By default, {\ACE} has a physical table size of $10^6$ words (i.e., $4
\times 10^6$ bytes in the default 32-bit environment). The number of
coset numbers in the table is the table size divided by the number of
columns. Although the number of coset numbers is limited to
$2^{31}-1$ (if the C `int' type is 32 bits), the table size can exceed
the $4$GByte 32-bit limit if a suitable machine is used.
\>`time:=<val>'{option time}@{option `time'}&
Maximum execution time in seconds; `<val>' must be an integer greater
than or equal to $-1$. (Shortest abbreviation: `ti'.)
The `time' command puts a time limit (in seconds) on the length of a
run. The default is $-1$ which is no time limit. If the argument is
$\ge0$ then the total elapsed time for this call is checked at the end
of each pass through the enumerator's main loop, and if it's more than
the limit the run is stopped and the current table returned.
Note that a limit of $0$ performs exactly one pass through the main
loop, since $0 \ge 0$.
The time limit is approximate, in the sense that the enumerator may
run for a longer, but never a shorter, time. So, if there is, e.g., a
big collapse (so that the time round the loop becomes very long), then
the run may run over the limit by a large amount.
*Notes:*
The time limit is CPU-time, not wall-time. As in all timing under
UNIX, the clock's granularity (usually $10$ milliseconds) and the
system load can affect the timing; so the number of main loop
iterations in a given time may vary.
\>`loop:=<val>'{option loop}@{option `loop'}&
Loop limit; `<val>' should be a non-negative integer.
The core enumerator is organised as a state machine, with each step
performing an ``action'' (i.e., lookahead, compaction) or a block of
actions (i.e., $|`ct'|$ coset number definitions, $|`rt'|$ coset
number applications). The number of passes through the main loop
(i.e., steps) is counted, and the enumerator can make an early return
when this count hits the value of `loop'. A value of $0$, the default,
turns this feature off.
*Guru Notes:*
You can do lots of really neat things using this feature, but you need
some understanding of the internals of {\ACE} to get real benefit from
it.
\>`path'{option path}@{option `path'}&
Turns on path compression.
To correctly process multiple concidences, a union-find must be
performed. If both path compression and weighted union are used, then
this can be done in essentially linear time (see, e.g., \cite{CLR90}).
Weighted union alone, in the worst-case, is worse than linear, but is
subquadratic. In practice, path compression is expensive, since it
involves many coset table accesses. So, by default, path compression
is turned off; it can be turned on by `path'. It has no effect on the
result, but may affect the running time and the internal statistics.
*Guru Notes:*
The whole question of the best way to handle large coincidence forests
is problematic. Formally, {\ACE} does not do a weighted union, since
it is constrained to replace the higher-numbered of a coincident pair.
In practice, this seems to amount to much the same thing! Turning
path compression on cuts down the amount of data movement during
coincidence processing at the expense of having to trace the paths and
compress them. In general, it does not seem to be worthwhile.
\index{dead coset (number)}
\>`compaction:=<val>'{option compaction}@{option `compaction'}&
Percentage of dead coset numbers to trigger compaction;
`<val>' should be an integer (percentage) in the integer range 0 to
100. (Shortest abbreviation: `com'.)
\index{dead coset (number)}
The option `compaction' sets the percentage of *dead* coset numbers
needed to trigger compaction of the coset table, during an
enumeration. A *dead* coset (number) is a coset number found to be
coincident with a smaller coset number. The default is 10 or 100,
depending on the strategy used (see Chapter~"Strategy Options for
ACE").
Compaction recovers the space allocated to coset numbers which are
flagged as dead. It results in a table where all the active coset
numbers are numbered contiguously from 1, and with the remainder of
the table available for new coset numbers.
The coset table is compacted when a definition of a coset number is
required, there is no space for a new coset number available, and
provided that the given percentage of the coset table contains dead
coset numbers. For example, if `compaction' = $20$ then compaction
will occur only if 20\% or more of the coset numbers in the table are
dead. An argument of 100 means that compaction is never performed,
while an argument of 0 means always compact, no matter how few dead
coset numbers there are (provided there is at least one, of course).
Compaction may be performed multiple times during an enumeration, and
the table that results from an enumeration may or may not be compact,
depending on whether or not there have been any coincidences since the
last compaction (or from the start of the enumeration, if there have
been no compactions).
*Notes:*
In some strategies (e.g., `hlt'; see~"option hlt") a lookahead phase
may be run before compaction is attempted. In other strategies (e.g.,
`sims := 3'; see~"option sims") compaction may be performed while
there are outstanding deductions; since deductions are discarded
during compaction, a final lookahead phase will (automatically) be
performed.
\index{dead coset (number)}
Compacting a table ``destroys'' information and history, in the sense
that the coincidence list is deleted, and the table entries for any
dead coset numbers are deleted.
\>`max:=<val>'{option max}@{option `max'}&
Sets the maximum coset number that can be defined;
`<val>' should be $0$ or an integer greater than or equal to 2.
By default (which is the case `max'${}=0$), all of the workspace is
used, if necessary, in building the coset table. So the table size (in
terms of the number of rows) is an upper bound on how many coset
numbers can be alive at any one time. The `max' option allows a limit
to be placed on how much physical table space is made available to the
enumerator. Enough space for at least two coset numbers (i.e., the
subgroup and one other) must be made available.
*Notes:*
If the `easy' strategy (see~"option easy") is selected, so that
`compaction' (see~"option compaction") is off (i.e.~set to 100) and
`lookahead' (see~"option lookahead") is off (i.e.~set to 0), and `max'
is set to a positive integer, then coset numbers are not reused, and
hence `max' bounds the *total* number `totcosets' (see Section~"Coset
Statistics Terminology") of coset numbers defined during an
enumeration.
On the other hand, if one (or both) of `compaction' or `lookahead' is
not off, then some reuse of coset numbers may occur, so that, for the
case where `max' is a positive integer, the value of `totcosets' may
be greater than `max'.
However, whenever `max' is set to a positive integer, both
*activecosets* (the number of *alive* coset numbers at the end of an
enumeration) and *maxcosets* (the maximum number of alive coset
numbers at any point of an enumeration) are bounded by `max'. See
Section~"Coset Statistics Terminology", for a discussion of the
terminology: *activecosets* and *maxcosets*.
\>`hole:=<val>'{option hole}@{option `hole'}&
Maximum percentage of holes allowed during an enumeration;
`<val>' should be an integer in the range $-1$ to 100.
(Shortest abbreviation: `ho'.)
This is an experimental feature which allows an enumeration to be
terminated when the percentage of holes in the table exceeds a given
value. In practice, calculating this is very expensive, and it tends
to remain constant or decrease throughout an enumeration. So the
feature doesn't seem very useful. The default value of $-1$ turns this
feature off. If you want more details, read the source code.
\enditems
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\Section{ACE Parameter Options controlling ACE Output}
\beginitems
\>`messages:=<val>'{option messages}@{option `messages'}
\>`monitor:=<val>'{option monitor}@{option `monitor'}&
Sets the verbosity of output from {\ACE}; <val> should be an integer.
(Shortest abbreviation of `messages' is `mess', and shortest
abbreviation of `monitor' is `mon'.)
By default, <val> = 0, for which {\ACE} prints out only a single line
of information, giving the result of each enumeration. If <val> is
non-zero then the presentation and the parameters are echoed at the
start of the run, and messages on the enumeration's status as it
progresses are also printed out. The absolute value of <val> sets the
frequency of the progress messages, with a negative sign turning hole
monitoring on. Note that, hole monitoring is expensive, so don't turn
it on unless you really need it.
Note that, ordinarily, one will not see these messages:
non-interactively, these messages are directed to file
`ACEData.outfile' (or <filename>, if option `aceoutfile :=
<filename>', or `ao := <filename>', is used), and interactively these
messages are simply not displayed. However, one can change this
situation both interactively and non-interactively by setting the
`InfoLevel' of `InfoACE' to 3 via
\beginexample
gap> SetInfoACELevel(3);
\endexample
Then {\ACE}'s messages are displayed prepended with ```\#I '''.
Please refer to Appendix~"The Meanings of ACE's output messages",
where the meanings of {\ACE}'s output messages are fully discussed.
\enditems
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\Section{ACE Parameter Options that give Names to the Group and Subgroup}
These options may be safely ignored; they only give names to the group
or subgroup within the {\ACE} output, and have no effect on the
enumeration itself.
\beginitems
\>`enumeration:=<string>'{option enumeration}@{option `enumeration'}&
Sets the `Group Name' to <string>; <string>, must of course be a
string. (Shortest abbreviation: `enum'.)
The {\ACE} binary has a two-word synonym for this option: `Group Name'
and this is how it is identified in the ``Run Parameters'' block of
the {\ACE} output when `messages' has a non-zero value. The default
`Group Name' is `"G"'.
\>`subgroup:=<string>'{option subgroup}@{option `subgroup'}&
Sets the `Subgroup Name' to <string>; <string> must of course be a
string. (Shortest abbreviation: `subg'.)
The default `Subgroup Name' is `"H"'.
\enditems
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\Section{Options for redirection of ACE Output}
\beginitems
\>`ao:=<filename>'{option ao}@{option `ao'}
\>`aceoutfile:=<filename>'{option aceoutfile!ao synonym}@{option `aceoutfile'}&
Redirects (`a'lters) `o'utput to <filename>; <filename> should be a
string.
Non-interactively, {\ACE}'s output is normally directed to a temporary
file whose full path is stored in `ACEData.outfile', which is parsed
to produce a coset table or a list of statistics. This option causes
{\ACE}'s output to be directed to <filename> instead, presumably
because the user wishes to see (and keep) data output by the {\ACE}
binary, other than the coset table output from
`ACECosetTableFromGensAndRels' or the statistics output by `ACEStats'.
Please refer to Appendix~"The Meanings of ACE's output messages",
where we discuss the meaning of the additional data to be found in the
{\ACE} binary's output. The option `aceoutfile' is a {\GAP}-introduced
synonym for `ao', that is translated to `ao' before submission to the
{\ACE} binary. Do not use option `aceoutfile' when running the
standalone directly. Happily, `ao' can also be regarded as mnemonical
for `aceoutfile'.
\enditems
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\Section{Other Options}
{\ACE} has a number of other options, but the {\GAP} user will not
ordinarily need them, since, in most cases, alternative interactive
functions exist. These remaining options have been relegated to
Appendix~"Other ACE Options". The options listed there may be used
both interactively and non-interactively, but many are probably best
used directly via the {\ACE} standalone.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%
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