poisson deklaracja warunków brzegowych

#include <iostream>
#include <math.h>
using namespace std;

const double b = 1;
const int n = 20;
const double pi=3.141592;

double f(double x, double y) { return 2; }
double u_exact(double x, double y) { return x*x; }



double g0(double x) { return 0.; }
double g1(double y) { return 1.0); }
double g2(double x) { return y(1-y)); }
double g3(double y) { return 0.0; }
double f(double x, double y) { return 6*x*y*(1-y)-2*x^3; }

double u_exact(double x, double y) { return x*x*cos(4*y); }


void PoissonOnSquare(double (*g[4])(double), double u[n+2][n+2], int numIter) {
     int i, j, k;
     double h;
     
     h = b/(n+1);
     for (i=0; i <=n+1; i++) {
         u[i][0]   = (*g[0])(i*h);
         u[n+1][i] = (*g[1])(i*h);
         u[i][n+1] = (*g[2])(i*h);
         u[0][i]   = (*g[3])(i*h);
     }
     for (i=1; i <= n; i++)
         for (j=1; j <= n; j++) u[i][j] = 0.0;
     
     for (k=1; k <= numIter; k++)
         for (i=1; i <= n; i++)
             for (j=1; j <= n; j++)
                 u[i][j] = 0.25*(u[i-1][j]+u[i+1][j]+u[i][j-1]+u[i][j+1]-h*h*f(i*h,j*h));
}

int main() {
    double (*g[4])(double), u[n+2][n+2];
    int i, j;
    
    g[0] = &g0; g[1] = &g1; g[2] = &g2; g[3] = &g3;
    
    PoissonOnSquare(g, u, 500);
    
    for (i=1; i <= n; i=i+4) {
        for (j=1; j <= n; j=j+4) { cout.precision(4); cout.width(10); cout << right << u[i][j]; }
        cout << "\n";
    }
    cout << "\n *** Rozwiązanie dokładne ***\n";
    for (i=1; i <= n; i=i+4) {
        for (j=1; j <= n; j=j+4) { cout.precision(4); cout.width(10); cout << right << u_exact(i*b/(n+1), j*b/(n+1))<< " "; }
        cout << "\n";
    }

    system("pause");
} 

czy dobrze zaimplementowałam warunki brzegowe w takim kodzie? bo chciałabym mieć :
x=0 -> a1=1, b1=0, c1=0
a dla x=1 -> a1=1,b1=0 i c1=y(1-y)