[galib] Bug in GADemeGA::nPopulations ?

[Nuissl, Tobias (ext.) ST/HZA-EWBP]

Dear Mr. Wall,

in my work with your Library GALib, I experienced some problem while using GADemeGA:

When using an arbitrary number of populations for deme (for example the default value of 10) in combination with an arbitrary number of individuals per population (which can be set via gaNpopulationSize), the number of populations for deme does (of course) not necessarily match the number of individuals in pop.

In the current version, GADemeGA::nPopulatio with n=npop does not do anything but returning that value (GADemeGA.C - line 252).

So in some cases there could happen an access violation while initializing the GEDeme object due to the copy process pop->individual(i).copy(deme[i]->best()) (GADemeGA.C - line 335) when the number of individuals in pop is smaller then the number of populations in deme.

In my opinion the function int GADemeGA::nPopulations(unsigned int n) (GADemeGA.C - lines 250-299) should be changed according to the red annotations below, to assure the numbers of populations and the individuals per population always fit each other (even when n=npop, where not necessarily npop=pop->size):

     int
     GADemeGA::nPopulations(unsigned int n) {
       if(n < 1 || n == npop) return npop;
       if(n < npop) {
         for(unsigned int i=n; i<npop; i++)
           delete deme[i];
         GAPopulation** ptmp = deme;
         deme = new GAPopulation* [n];
         memcpy(deme, ptmp, n * sizeof(GAPopulation*));
         delete [] ptmp;

         GAStatistics* stmp = pstats;
         pstats = new GAStatistics[n];
         for(unsigned int j=0; j<n; j++)
           pstats[j] = stmp[j];
         delete [] stmp;

         int* rtmp = nrepl;
         nrepl = new int[n];
         memcpy(nrepl, rtmp, n * sizeof(int));
         delete [] rtmp;

         npop = n;
       }
       else if (n > npop) {
         GAPopulation** ptmp = deme;
         deme = new GAPopulation* [n];
         memcpy(deme, ptmp, npop * sizeof(GAPopulation*));
         delete [] ptmp;
         for(unsigned int i=npop; i<n; i++)
           deme[i] = new GAPopulation(*deme[GARandomInt(0,npop-1)]);

         GAStatistics* stmp = pstats;
         pstats = new GAStatistics[n];
         for(unsigned int j=0; j<npop; j++)
           pstats[j] = stmp[j];
         delete [] stmp;

         int* rtmp = nrepl;
         nrepl = new int[n];
         memcpy(nrepl, rtmp, npop * sizeof(int));
         for(unsigned int k=npop; k<n; k++)
           nrepl[k] = nrepl[0];

         npop = n;
       }
       params.set(gaNnPopulations, (unsigned int)n);
       pop->size(npop);
       return npop;
     }

I am looking forward to receiving an answer with your opinion to this situation.

Best regards

Tobias Nuißl
Technische IT · CAE-Werkzeuge · Programmentwicklung (ext.)

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