21. Parallel Computation - Core Functions
  
      | ChildProcess() ChildProcess("computer.ac.wales") This starts a GAP session as a child process and returns a stream to the child process. If no argument is given then the child process is created on the local machine; otherwise the argument should be the address of a remote computer for which ssh has been configured to require no password from the user. (To configure ssh so that the user can login without a password prompt from "thishost" to "remotehost" either consult "man ssh" or - open a shell on thishost - cd .ssh - ls -> if id_dsa, id_rsa etc exists, skip the next two steps! - ssh-keygen -t rsa - ssh-keygen -t dsa - scp *.pub user@remotehost:~/ - ssh remotehost -l user - cat id_rsa.pub >> .ssh/authorized_keys - cat id_dsa.pub >> .ssh/authorized_keys - rm id_rsa.pub id_dsa.pub - exit You should now be able to connect from "thishost" to "remotehost" without a password prompt.) | 
      | ChildClose(s) This closes the stream s to a child GAP process.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              | 
      | ChildCommand("cmd;",s) This runs a GAP command "cmd;" on the child process accessed by the stream s. Here "cmd;" is a string representing the command.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | 
      |  NextAvailableChild(L) Inputs a list L of child processes and returns a child in L which is ready for computation (as soon as such a child is available).                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 
      |  IsAvailableChild(s) Inputs a child process s and returns true if s is currently available for computations, and false otherwise.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | 
      |  ChildPut(A,"B",s) This copies a GAP object A on the parent process to an object B on the child process s. (The copying relies on the function PrintObj(A); )                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 
      |  ChildGet("A",s) This functions copies a GAP object A on the child process s and returns it on the parent process. (The copying relies on the function PrintObj(A); )                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       | 
      | HAPPrintTo("file",R) Inputs a name "file" of a new text file and a HAP object R. It writes the object R to "file". Currently this is only implemented for R equal to a resolution.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 
      | HAPRead("file",R) Inputs a name "file" containing a HAP object R and returns the object. Currently this is only implemented for R equal to a resolution.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |