source: git/Singular/LIB/factor.lib @ 90df7c

///////////////////////////////////////////////////////////////////////////////
version="version factor.lib 4.0.0.0 Jun_2013 "; // $Id$
info="
LIBRARY:  factor.lib    PROCEDURES FOR CALLING THE REDUCE FACTORIZER

 delete_dollar(s)       return the string s with '$' deleted
 reduce_factor(f)       list of factors of f, calling REDUCE (UNIX only)
";

///////////////////////////////////////////////////////////////////////////////

proc delete_dollar ( string s )
"USAGE:   delete_dollar(s);  s = string
RETURN:  string, with '$' replaced by ' '
EXAMPLE: example delete_dollar; shows an example
"
{
   while( s[size(s)]=="$" and size(s)!=1 ) { s=s[1,size(s)-1]; }
   while( s[1]=="$" and size(s)!=1 )       { s=s[2,size(s)-1]; }
   if( size(s)==1 and s[1]=="$" )          { return(""); }
   int i=find(s,"$");
   while( i!=0 )
   {
     s=s[1,i-1]+s[i+1,size(s)-i];
     i=find(s,"$");
   }
   return(s);
}
example
{ "EXAMPLE:"; echo = 2;
  string s = "123$456$";
  delete_dollar(s);
  delete_dollar(s)+"789";
}
///////////////////////////////////////////////////////////////////////////////

proc reduce_factor ( poly f )
"USAGE:   reduce_factor(f);  f = poly
RETURN:  list, the factors of f
NOTE:    due to a limitation of REDUCE, multivariate polynomials can only
         be factorized in characteristic 0
         This proc runs under UNIX only
EXAMPLE: example reduce_factor; shows an example
"
{
  string pid = string( system( "pid" ) );
  string outname = "/tmp/singred." + pid + ".out";
  string scriptname = "/tmp/singred." + pid + ".sh";
  int n = char( basering );
  int shortOutput = short;
  short = 0;
  write (scriptname,"#!/bin/sh
                    $reduce/reduce >/dev/null <<EOF
                    off nat$ off echo$ setmod " + string( n ) + "$
                    erg:=factorize(",f,")$
                    out \"" + outname + "\"$
                    write(\"list result;\")$
                    counter:=1$
                    for each a in erg do begin
                        write(\"result[\",counter,\"]=\",a,\";\");
                        counter:=counter+1;
                    end;
                    shut \"" + outname + "\";
                    quit$
               EOF");
  system( "sh", "chmod 700 " + scriptname );
  system( "sh", scriptname );
  string resultstring = read( outname );
  if ( resultstring <> "" )
  {
    resultstring = delete_dollar( resultstring );
    execute(resultstring);
  }
  // remove tmp-files after usage */
  system( "sh", "/bin/rm " + outname );
  system( "sh", "/bin/rm " + scriptname );
  short = shortOutput;
  return( result );
}
example
{ "EXAMPLE:"; echo = 2;
  ring r=0,(x,y,z),lp;
  poly f=(x+y)*(y+z)^2*(z+x);
  f;
  list L=reduce_factor(f);
  L;
}