hopfield model

gistfile1.cpp

#include <cstdio>
#include <cmath>
#include <ctime>
#include <cassert>
#include <stdint.h>
#include <vector>

#include <boost/numeric/ublas/vector.hpp>
#include <boost/numeric/ublas/matrix.hpp>

using namespace boost::numeric;

static const int M = 2;
static const int N = 8;

int main()
{

    // patterns

    ublas::vector<int> P[M];

    ublas::vector<int> p(N);

    p(0) = +1;
    p(1) = +1;
    p(2) = +1;
    p(3) = +1;
    p(4) = -1;
    p(5) = -1;
    p(6) = -1;
    p(7) = -1;

    P[0] = p;

    p(0) = +1;
    p(1) = +1;
    p(2) = -1;
    p(3) = -1;
    p(4) = +1;
    p(5) = +1;
    p(6) = -1;
    p(7) = -1;

    P[1] = p;

    // learning phase

    ublas::matrix<int> W(N, N);
    
    for(int i = 0; i < N; ++i)
    {
        for(int j = 0; j < N; ++j)
        {
            int sum = 0;

            if (i != j)
            {
                for(int s = 0; s < M; ++s)
                {
                    sum += P[s](i) * P[s](j);
                }
            }

            W(i, j) = sum;
        }
    }


    // initial pattern

    ublas::vector<int> u(N);

    u(0) = +1;
    u(1) = +1;
    u(2) = -1;
    u(3) = -1;
    u(4) = +1;
    u(5) = -1;
    u(6) = +1;
    u(7) = +1;


    // recovering

    bool isUnstable;

    do
    {
        isUnstable = false;

        ublas::vector<int> v = u;

        for(int i = 0; i < N; ++i)
        {
            printf("u[%d] = %d\n", i, u(i));
        }

        int E = 0;

        for(int i = 0; i < N; ++i)
            for(int j = 0; j < N; ++j)
                E += - W(i,j) * u(i) * u(j);

        printf("E = %d\n", E / 2);

        printf("-------------------\n");
        
        for(int i = 0; i < N; ++i)
        {
            int sum = 0;

            for(int j = 0; j < N; ++j)
            {
                sum += W(i, j) * v(j);
            }

            u(i) = (sum >= 0) ? +1 : -1;

            if (u(i) != v(i))
                isUnstable = true;
        }
    }
    while(isUnstable);

    return 0;
}