# Help with my GA

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I've been working on getting this program to work for quite a while. It is supposed to solve the problem "52 = a + 2b + 3c". Please help me to get it to work. It solves the problem sometimes, but other times it just loops the same number until the program ends or it crashes. I am almost positive it is something wrong with the "Choose_Mate()" function
#include <iostream>
#include <math.h>
#include <fstream>
#include <stdlib.h>
#include <windows.h>

using namespace std;

#define MAXPOP 10
#define MAXALL 3
// 52 = a + 2b + 3c

ofstream fout;
void start_pop(), fitness(), probability(), choose_mate(), mutate();

class POPULATION
{
public:
int FitSum;
int ProbSum;
int generation;
}population;

class INDIVIDUAL
{
public:
int fitness;
int probability;
int allele[3];

int mother;
int father;

}individual[MAXPOP];

int main()
{

srand(GetTickCount());

fout.open("stats.txt");
start_pop();

cout << "Simulating Population\n";

while(1)
{
population.FitSum = 0;
population.ProbSum = 0;
population.generation++;
fitness();
probability();
choose_mate();
mutate();
}
return 0;
}

void fitness()
{
int sum = 0;

if(population.generation > 1000)
{
system("pause");
exit(0);
}

for(int i = 0; i < MAXPOP; i++)
{
individual.fitness = 100 - (abs(52 - (individual.allele[0] + (2 * individual.allele[1]) + (3 * individual.allele[2]))));
population.FitSum += individual.fitness;

if(individual.fitness == 100)
{
fout << "+++++++++++++++++++++++++++\n";
fout << "+SOLVED:\n";
fout << "+A = " << individual.allele[0] << endl;
fout << "+B = " << individual.allele[1] << endl;
fout << "+C = " <<individual.allele[2] << endl;
fout << "+Generation: " << population.generation;
fout << "\n+++++++++++++++++++++++++++\n";
cout << "\nSolved\n";
system("pause");
exit(0);
}
}

/*for(int i = 0; i < MAXPOP; i++)
{
if(individual.fitness > (population.FitSum / MAXPOP))
{
individual.fitness += 20;
}

if(individual.fitness < (population.FitSum / MAXPOP))
{
individual.fitness -= 20;
}
} */
return;
}

void probability()
{
for(int i = 0; i < (MAXPOP); ++i)
{
individual.probability = individual.fitness + population.ProbSum;
population.ProbSum += individual.fitness;
}
return;
}

void choose_mate()
{
INDIVIDUAL newpop[MAXPOP];
int pop = 0;
bool fmalleles[3];

while(pop < MAXPOP)
{
fmalleles[rand() % 3] = true;
fmalleles[rand() % 3] = true;
bool father = false;
bool mother = false;
int RandFather = (rand() % population.ProbSum);
int RandMother = (rand() % population.ProbSum);

for(int i = 0; i < (MAXPOP); i++)
{
if(RandFather > individual.probability && RandFather < individual[i + 1].probability || RandFather == individual.probability)
{
father = true;
int trans = 0;
while(trans < 3)
{
if(fmalleles[trans] == true)
{
newpop[pop].allele[trans] = individual.allele[trans];
}
trans++;
}
}

if(RandMother > individual.probability && RandMother < individual[i + 1].probability || RandMother == individual.probability)
{
mother = true;
int trans = 0;
while(trans < 3)
{
if(fmalleles[trans] == false)
{
newpop[pop].allele[trans] = individual.allele[trans];
}
trans++;
}
}

}

if(mother == false || father == false)
{
pop -= 1;
}
pop++;
}
for(int i = 0; i < (MAXPOP); i++)
{
individual = newpop;
}
return;
}

void start_pop()
{
for(int i = 0; i < (MAXPOP); i++)
{
for(int j = 0; j < 3; j++)
{
individual.allele[j] = rand() % 10 + 1;
}
}
return;
}

void mutate()
{
int pop = 0;
while(pop < MAXPOP)
{
int allele = rand() % 3;
int pm = rand() % 1;
int mutate = rand() % 50;
if(mutate == 15 || mutate == 21)
{
if(pm == 0)
{
individual[pop].allele[allele] += 1;
}
else
{
individual[pop].allele[allele] -= 1;
}
}
pop++;
}
return;
}



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At first glance:
- You have an off-by-one error regarding MAXPOP (you access newpop[MAXPOP] in the loop when you shouldn't)
- No idea what 'fmalleles' does - is this your crossover operator, effectively? - but it appears that you fail to initialise the array to begin with and then very quickly turn each of the 3 members to true
- "RandFather > individual.probability && RandFather < individual[i + 1].probability || RandFather == individual.probability" should probably be "RandFather >= individual.probability && RandFather < individual[i + 1].probability"

Personally I would clean up parts of that function by moving key aspects into other distinct functions: eg. one to perform the selection, another one to perform the cross over, etc.

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Thanks ill try that out now.
I do not understand what you mean here
"You have an off-by-one error regarding MAXPOP (you access newpop[MAXPOP] in the loop when you shouldn't"

Even without that part I didn't understand it works, so far as I can tell 100% of the time now. Thank you a lot.

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individual[MAXPOP] - you have MAXPOP individuals, from 0 to MAXPOP-1.

for(int i = 0; i < (MAXPOP); i++) - That means i can equal MAXPOP-1.

if(RandFather > individual.probability && RandFather < individual[i + 1] - that means you access individual[MAXPOP-1 + 1], which doesn't exist.

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