Question

I have written a global version of Particle Swarm Optimization algorithm in C++.
I tried to write it exactly as same as my MATLAB PSO code that have written before, but this code generates different and so worst answers.
The MATLAB code is:

clear all;

numofdims = 30;
numofparticles = 50;
c1 = 2;
c2 = 2;
numofiterations = 1000;
V = zeros(50, 30);
initialpop = V;
Vmin = zeros(30, 1);
Vmax = Vmin;
Xmax = ones(30, 1) * 100;
Xmin = -Xmax;
pbestfits = zeros(50, 1);
worsts = zeros(50, 1);
bests = zeros(50, 1);
meanfits = zeros(50, 1);
pbests = zeros(50, 30);

initialpop = Xmin + (Xmax - Xmin) .* rand(numofparticles, numofdims);

X = initialpop;
fitnesses = testfunc1(X);
[minfit, minfitidx] = min(fitnesses);
gbestfit = minfit;
gbest = X(minfitidx, :);

for i = 1:numofdims
    Vmax(i) = 0.2 * (Xmax(i) - Xmin(i));
    Vmin(i) = -Vmax(i);
end

for t = 1:1000
    w = 0.9 - 0.7 * (t / numofiterations);

    for i = 1:numofparticles
        if(fitnesses(i) < pbestfits(i))
            pbestfits(i) = fitnesses(i);
            pbests(i, :) =  X(i, :);
        end
    end
    for i = 1:numofparticles
        for j = 1:numofdims
            V(i, j) = min(max((w * V(i, j) + rand * c1 * (pbests(i, j) - X(i, j))...
                + rand * c2 * (gbest(j) - X(i, j))), Vmin(j)), Vmax(j));
            X(i, j) = min(max((X(i, j) + V(i, j)), Xmin(j)), Xmax(j));
        end
    end

    fitnesses = testfunc1(X);
    [minfit, minfitidx] = min(fitnesses);
    if(minfit < gbestfit)
        gbestfit = minfit;
        gbest = X(minfitidx, :);
    end

    worsts(t) = max(fitnesses);
    bests(t) = gbestfit;
    meanfits(t) = mean(fitnesses);
end

In which, testfunc1 is:

function [out] = testfunc1(R)
    out = sum(R .^ 2, 2);
end

The C++ code is:

#include <cstring>
#include <iostream>
#include <cmath>
#include <algorithm>
#include <ctime>

#define rand_01 ((float)rand() / (float)RAND_MAX)

const int numofdims = 30;
const int numofparticles = 50;

using namespace std;

void fitnessfunc(float X[numofparticles][numofdims], float fitnesses[numofparticles])
{
    memset(fitnesses, 0, sizeof (float) * numofparticles);
    for(int i = 0; i < numofparticles; i++)
    {
        for(int j = 0; j < numofdims; j++)
        {
            fitnesses[i] += (pow(X[i][j], 2));
        }
    }
}

float mean(float inputval[], int vallength)
{
    int addvalue = 0;
    for(int i = 0; i < vallength; i++)
    {
        addvalue += inputval[i];
    }
    return (float)(addvalue / vallength);
}

void PSO(int numofiterations, float c1, float c2,
              float Xmin[numofdims], float Xmax[numofdims], float initialpop[numofparticles][numofdims],
              float worsts[], float meanfits[], float bests[], float *gbestfit, float gbest[numofdims])
{
    float V[numofparticles][numofdims] = {0};
    float X[numofparticles][numofdims];
    float Vmax[numofdims];
    float Vmin[numofdims];
    float pbests[numofparticles][numofdims];
    float pbestfits[numofparticles];
    float fitnesses[numofparticles];
    float w;
    float minfit;
    int   minfitidx;

    memcpy(X, initialpop, sizeof(float) * numofparticles * numofdims);
    fitnessfunc(X, fitnesses);
    minfit = *min_element(fitnesses, fitnesses + numofparticles);
    minfitidx = min_element(fitnesses, fitnesses + numofparticles) - fitnesses;
    *gbestfit = minfit;
    memcpy(gbest, X[minfitidx], sizeof(float) * numofdims);

    for(int i = 0; i < numofdims; i++)
    {
        Vmax[i] = 0.2 * (Xmax[i] - Xmin[i]);
        Vmin[i] = -Vmax[i];
    }

    for(int t = 0; t < 1000; t++)
    {
        w = 0.9 - 0.7 * (float) (t / numofiterations);

        for(int i = 0; i < numofparticles; i++)
        {
            if(fitnesses[i] < pbestfits[i])
            {
                pbestfits[i] = fitnesses[i];
                memcpy(pbests[i], X[i], sizeof(float) * numofdims);
            }
        }
        for(int i = 0; i < numofparticles; i++)
        {
            for(int j = 0; j < numofdims; j++)
            {
                V[i][j] = min(max((w * V[i][j] + rand_01 * c1 * (pbests[i][j] - X[i][j])
                                   + rand_01 * c2 * (gbest[j] - X[i][j])), Vmin[j]), Vmax[j]);
                X[i][j] = min(max((X[i][j] + V[i][j]), Xmin[j]), Xmax[j]);
            }
        }

        fitnessfunc(X, fitnesses);
        minfit = *min_element(fitnesses, fitnesses + numofparticles);
        minfitidx = min_element(fitnesses, fitnesses + numofparticles) - fitnesses;
        if(minfit < *gbestfit)
        {
            *gbestfit = minfit;
            memcpy(gbest, X[minfitidx], sizeof(float) * numofdims);
        }

        worsts[t] = *max_element(fitnesses, fitnesses + numofparticles);
        bests[t] = *gbestfit;
        meanfits[t] = mean(fitnesses, numofparticles);
    }


}

int main()
{
    time_t t;
    srand((unsigned) time(&t));

    float xmin[30], xmax[30];
    float initpop[50][30];
    float worsts[1000], bests[1000];
    float meanfits[1000];
    float gbestfit;
    float gbest[30];
    for(int i = 0; i < 30; i++)
    {
        xmax[i] = 100;
        xmin[i] = -100;
    }
    for(int i = 0; i < 50; i++)
        for(int j = 0; j < 30; j++)
        {
            initpop[i][j] = rand() % (100 + 100 + 1) - 100;
        }

    PSO(1000, 2, 2, xmin, xmax, initpop, worsts, meanfits, bests, &gbestfit, gbest);

    cout<<"fitness: "<<gbestfit<<endl;
    return 0;
}

I have debugged two codes many times but can not find the difference which makes answers different.
It is making me crazy!
May you help me please?

Update:

Please consider that, the function mean is just used for reporting some information and is not used in the optimization procedure.

Answer 1

You’ve got integer division in the following line
w = 0.9 - 0.7 * (float) (t / numofiterations);
w will be 0.2 for every iteration, change it to
w = 0.9 - 0.7 * t / numofiterations;

The first multiplication will automatically promote t to a double the division should then promote numof iterations to a double.

The parenthesis means it will be done first and therefore not be promoted as wo integers is involved in the division.