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<title>ploticus: proc curvefit</title>
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<td><br><h2>proc curvefit</h2></td>
<td align=right>
<small>
<a href="../doc/welcome.html"><img src="../doc/ploticus.gif" border=0></a><br>
Version 2.41 Mar2009
</small><br><a href="../doc/scripthome.html">Scripts</a>
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<td>
<br>
<br>
<title>Manual page for proc_curvefit(PL)</title>
</head>
<body>
<center>
<img src="../gallery/curvefit3.gif">
</center>
<p>
<b>proc curvefit</b> uses the
<a href="dataformat.html#currentds">
current data set
</a>
to compute a curve which it then renders in the
<a href="areadef.html">
current plotting area.<tt> </tt>
</a>
Available curve types are: moving average, average, linear regression, bspline, and interpolated curves.<tt> </tt>
Typical uses are to clarify overall trends in the data, or for smoothing.<tt> </tt>
(If you just want to draw a line connecting your data points, without any smoothing, use
<a href="lineplot.html">
proc lineplot.)
</a>
The data do not have to be in X order.. they will be sorted on X as part of the process
(except with the interpolated curve type). See also the
<a href="../gallery/gall.curvefit.html">
gallery curvefit examples.<tt> </tt>
</a>
<p>
Limitations:
The maximum number of input points for a bspline curve is 100.
The default maxiumum number of input points for all other curve types
is 1000.. to raise this limit use the proc curvefit attribute <tt>maxinpoints</tt>.<tt> </tt>
Generated curve points are placed into the plotting vector; its size can
be controlled using command line argument <tt>-maxvect</tt>.<tt> </tt>
<br><br><br>
<h2>Attributes</h2>
The <tt>yfield</tt> attribute MUST be specified.<tt> </tt>
<p>
<b>yfield</b>
<a href="attributetypes.html#dfield">
dfield
</a>
<dl>
<dt> <dd>
Data field to use for Y values. Example: <tt>yfield: 1</tt>
<br><br>
</dl>
<p>
<b>xfield</b>
<a href="attributetypes.html#dfield">
dfield
</a>
<dl>
<dt> <dd>
Data field to use for X values.<tt> </tt>
If not given, sequential unit locations in X will be used.<tt> </tt>
Example: <tt>xfield: 4</tt>
<br><br>
</dl>
<p>
<b>curvetype</b>
<tt>movingavg</tt> | <tt>regression</tt> | <tt>bspline</tt> | <tt>avg</tt> | <tt>interpolated</tt>
<dl>
<dt> <dd>
The type of curve fitting computation to perform.
<dt> <dd>
<b>movingavg</b> - for each point, it takes the average of the current point and <i>n</i>-1
points to the left (or as many points as are available).<tt> </tt>
<i>n</i> is controlled by the <tt>order</tt> attribute.<tt> </tt>
Often used in finance.<tt> </tt>
<dt> <dd>
<b>regression</b> - Computes the linear regression for the set of points. The result will be a
straight line expressing the relationship between X and Y. Often used with scatterplots.<tt> </tt>
The variables REGRESSION_LINE and CORRELATION will be set (see VARIABLES above).<tt> </tt>
<dt> <dd>
<b>bspline</b> - draws a curve using the bspline algorithm. The <tt>order</tt> and <tt>resolution</tt>
attributes control the appearance of the result. May be used to fit a curve to a histogram.<tt> </tt>
<dt> <dd>
<b>avg</b> - similar to movingavg except that it also includes <i>n</i>-1 points to the right
of the current point (or as many points as are available) in the average.
Thus, for a point that is far from either edge, 2<i>n</i>-1 points will be averaged.<tt> </tt>
<dt> <dd>
<b>interpolated</b> - a spline interpolation between the given data points, ie. the curve will pass through
all input data points (this type is new in version 2.20, code contibuted by Oliver Koch)
<dt> <dd>
Example: <tt>curvetype: movingavg</tt>
<br><br>
</dl>
<p>
<b>maxinpoints</b>
n
<dl>
<dt> <dd>
Maximum number of input points for curve types other than bspline. Default is 1000. (ver 2.30+)
<br><br><br>
</dl>
<h2>Details of curve appearance</h2>
<p>
<b>order</b>
<i>n</i>
<dl>
<dt> <dd>
For bspline curves, this is a value between 2 and 20; a lower value
yields a more jagged curve, while a higher value gives a smoother curve.<tt> </tt>
The number of data points must be at least this value for a bspline curve
to be possible.<tt> </tt>
<dt> <dd>
For movingavg curves, this defines the number of points
to include in each average computation. For avg curves, 2<i>n</i> - 1
points will be considered, where <i>n</i> = the <tt>order</tt> value.<tt> </tt>
<dt> <dd>
This attribute has no effect with regression or interpolated curve.<tt> </tt>
<dt> <dd>
Default order for either type of curve is 4.<tt> </tt>
<dt> <dd>
Example: <tt>order: 8</tt>
<br><br>
</dl>
<p>
<b>resolution</b>
<i>n</i>
<dl>
<dt> <dd>
Only relevant for bspline curves.
For every input point, <i>n</i> result points will be generated.<tt> </tt>
Default is 5.0.<tt> </tt>
<br><br>
</dl>
<p>
<b>linedetails</b>
<a href="linedetails.html">
linedetails
</a>
<dl>
<dt> <dd>
Appearance details for the curve.<tt> </tt>
Note that dash patterns may not be effective with generated curves (other than regression curves)
because of point density.<tt> </tt>
<br>
Example: <tt>linedetails: color=red width=2.0 </tt>
<br><br>
</dl>
<p>
<b>xsort</b>
<tt>yes | no</tt>
<dl>
<dt> <dd>
Whether or not to sort the input data on <tt>xfield</tt>
before generating curves of the <tt>interpolated</tt> type.<tt> </tt>
Default is <tt>no</tt>.<tt> </tt>
<br><br><br>
</dl>
<h2>Range control & selecting data rows</h2>
<p>
<b>select</b>
<a href="select.html">
select expression
</a>
<dl>
<dt> <dd>
Allows selected data points to be included in curve computation.<tt> </tt>
<br>
Example: <tt>select: @@3 > 0</tt>
<br><br>
</dl>
<p>
<b>calcrange</b>
<i>min</i>
[<i>max</i>]
<dl>
<dt> <dd>
Data within this X range will be included in curve calculation.<tt> </tt>
If only one value is given, it will be taken as the range
minima and the maxima will be the plottable maxima.<tt> </tt>
If not specified all data rows will be included.<tt> </tt>
<br><br>
</dl>
<p>
<b>linerange</b>
<i>min</i>
[<i>max</i>]
<dl>
<dt> <dd>
Controls the X range (in scaled units) within which the curve will be rendered.<tt> </tt>
Data points falling outside this range will not be rendered.<tt> </tt>
If accumulation is being done, points outside the range will contribute
to the accumulated total.<tt> </tt>
If only one value is given, it will be taken as the range
minima and the maxima will be the plottable maxima.<tt> </tt>
If not specified all data rows will be plotted.<tt> </tt>
<dt> <dd>
For regression curves, this attribute may be used to limit
the X range of the regression line, or to create a regression line that extends
beyond the X range of the data.
In this case, <i>min</i> and <i>max</i> should both be given.<tt> </tt>
<dt> <dd>
Example: <tt>linerange: 1</tt>
<br><br>
</dl>
<p>
<b>clip</b>
<tt>yes | no</tt>
<dl>
<dt> <dd>
Default is <tt>no</tt>. If set to <tt>yes</tt>, generated curve will be clipped to the
plotting area in Y. (Regression curves are always clipped.) (2.30+)
<br><br><br>
</dl>
<h2>Legend</h2>
<p>
<b>legendlabel</b>
<a href="attributetypes.html#text">
text
</a>
<dl>
<dt> <dd>
A label to be associated with the curve in the legend.<tt> </tt>
<b>proc legend</b> must be executed later in order to
render the legend.<tt> </tt>
The <tt>\n</tt> construct can be used to force a line break
or the label can be wordwrapped using proc legend wraplen attribute (2.32+).<tt> </tt>
If
<a href="getdata.html">
proc getdata field names
</a>
are being used,
the special symbol <tt>#usefname</tt> causes the field name of <tt>yfield</tt>
to be automatically used as the legend label (2.04+).<tt> </tt>
<br>
Example: <tt>legendlabel: Northeast region</tt>
<br>
Example: <tt>legendlabel: #usefname</tt>
<br><br><br>
</dl>
<h2>Accessing the coordinates of the generated curve</h2>
<p>
<b>showresults</b>
<tt>yes</tt> | <tt>no</tt>
<dl>
<dt> <dd>
If <tt>yes</tt>, a listing of the points in the computed curve will
be written to the diagnostic stream (-diag).<tt> </tt>
<br><br>
</dl>
<p>
<b>statsonly</b>
<tt>yes</tt> | <tt>no</tt>
<dl>
<dt> <dd>
If <tt>yes</tt>, don't draw the result curve. This is for situations where the user only wants
the computed curve values (<tt>showresults</tt>) or the
REGRESSION_LINE and CORRELATION variables to be set.<tt> </tt>
<br><br><br>
</dl>
<h2>Variables that are set by proc curvefit</h2>
<p>
<b>REGRESSION_LINE</b>
<dl>
<dt> <dd>
If curvetype is <tt>regression</tt>, this variable will be set to display
the formula for the regression line.<tt> </tt>
</dl>
<p>
<b>CORRELATION</b>
<dl>
<dt> <dd>
If curvetype is <tt>regression</tt>, this variable will be set to display
the Pearson correlation coefficient (r), which ranges from -1.0 to 1.0, where
1.0 is a strong correlation (positive slope), -1.0 is a strong correlation
(negative slope), and 0 is no correlation.<tt> </tt>
</dl>
<p>
<b>XFINAL</b> and <b>YFINAL</b>
<dl>
<dt> <dd>
are set to the final location (in scaled space) of the end of the drawn curve.<tt> </tt>
<br>
<br>
</td></tr>
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<a href="../doc/Copyright.html">Copyright Steve Grubb</a>
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