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GAP 4.8.9 installation with standard packages -- copy to your CoCalc project to get it

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/****************************************************************************

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**

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*A  collect_comm.c              ANUPQ source                   Eamonn O'Brien

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**

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*Y  Copyright 1995-2001,  Lehrstuhl D fuer Mathematik,  RWTH Aachen,  Germany

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*Y  Copyright 1995-2001,  School of Mathematical Sciences, ANU,     Australia

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**

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*/

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#include "pq_defs.h"

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#include "pcp_vars.h"

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#include "constants.h"

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#include "pq_functions.h"

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#include "pretty_filterfns.h"

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#include "word_types.h"

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/* collect a commutator relation in the defining generators of the group */

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void collect_def_comm(int ptr, int cp, struct pcp_vars *pcp)

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{

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   register int *y = y_address;

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   register int cp1, cp2, cp3, cp4, result;

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   register int lastg = pcp->lastg;

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   register int total;

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   int disp = 0;

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   int depth;

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   int exp;

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   cp1 = pcp->submlg - lastg - 2;

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   cp2 = cp1 - lastg;

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   cp3 = cp2 - lastg;

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   cp4 = cp3 - lastg;

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   result = cp4 - lastg;

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   /* fudge the value of submlg because of possible call to power */

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   total = 6 * lastg + 6;

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   pcp->submlg -= total;

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   depth = -y[ptr] - 1;

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   exp = y[ptr + 1];

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   collect_defining_generator(ptr + 2, cp2, pcp);

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   copy(cp2, lastg, cp3, pcp);

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   disp = 0;

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   while (--depth > 0) {

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      ++disp;

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      collect_defining_generator(ptr + 2 + disp, cp1, pcp);

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      copy(cp1, lastg, cp4, pcp);

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      /* solve the equation (ba) * x = ab to obtain [a, b] */

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      find_commutator(cp1, cp2, cp3, cp4, result, pcp);

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      copy(result, lastg, cp2, pcp);

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      copy(result, lastg, cp3, pcp);

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   }

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   power(exp, result, pcp);

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#ifdef DEBUG

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   /* print the commutator */

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   setup_word_to_print("commutator", result, pcp->lused, pcp);

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#endif

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   /* copy result to cp */

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   copy(result, lastg, cp, pcp);

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   /* reset the value of submlg */

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   pcp->submlg += total;

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}

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/* collect value of defining generator stored at y[ptr] to

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   storage location cp */

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void collect_defining_generator(int ptr, int cp, struct pcp_vars *pcp)

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{

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   register int *y = y_address;

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   register int lastg = pcp->lastg;

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   int i, generator, genval;

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#ifdef DEBUG

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   int j, word_len;

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#endif

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   /* zero out lastg entries in array in order to store result */

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   for (i = 1; i <= lastg; ++i)

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      y[cp + i] = 0;

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   generator = y[ptr];

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   genval = y[pcp->dgen + generator];

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   /* check for illegal defining generators */

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   if (abs(generator) > pcp->ndgen || generator == 0)

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      report_error(0, generator, 0);

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#ifdef DEBUG

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   if (genval > 0)

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      printf("%d %d\n", generator, genval);

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   else if (genval < 0) {

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      printf("%d %d ", generator, y[-genval]);

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      word_len = y[-genval + 1];

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      for (j = 1; j <= word_len; ++j)

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         printf(" %d", y[-genval + 1 + j]);

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   } else

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      printf("generator %d is trivial\n", generator);

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#endif

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   collect(genval, cp, pcp);

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#ifdef DEBUG

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   print_array(y, cp, cp + pcp->lastg + 1);

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#endif

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}

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