find_image.c

/****************************************************************************
**
*A  find_image.c                ANUPQ source                   Eamonn O'Brien
**
*Y  Copyright 1995-2001,  Lehrstuhl D fuer Mathematik,  RWTH Aachen,  Germany
*Y  Copyright 1995-2001,  School of Mathematical Sciences, ANU,     Australia
**
*/

#include "pq_defs.h"
#include "pcp_vars.h"
#include "pga_vars.h"
#include "pq_functions.h"

/* find the image of the allowable subgroup having supplied label under
   the action of automorphism; compute and return its label */

int
find_image(int label, int **auts, struct pga_vars *pga, struct pcp_vars *pcp)
{
   int index;
   int **A;
   int **Image, **Image_transpose;
   int **S, **S_transpose;
   int *subset;
   int K;

   subset = allocate_vector(pga->s, 0, 0);

   A = allocate_matrix(pga->q, pga->q, 0, FALSE);
   assemble_matrix(A, pga->q, auts, pcp);

   S = label_to_subgroup(&index, &subset, label, pga);
   S_transpose = transpose(S, pga->s, pga->q);
   Image_transpose =
       multiply_matrix(A, pga->q, pga->q, S_transpose, pga->s, pga->p);
   Image = transpose(Image_transpose, pga->q, pga->s);
   K = echelonise_matrix(Image, pga->s, pga->q, pga->p, subset, pga);

   free_matrix(A, pga->q, 0);
   free_matrix(S, pga->s, 0);
   free_matrix(S_transpose, pga->q, 0);
   free_matrix(Image_transpose, pga->q, 0);

   label = subgroup_to_label(Image, K, subset, pga);
   free_matrix(Image, pga->s, 0);
   free_vector(subset, 0);

   return label;
}