co oznaczają te kody?

 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, 50);
    
    for (i=1; i <= n; i++) {
        for (j=1; j <= n; j++) { cout.precision(4); cout.width(10); cout << right << u[i][j]; }
        cout << "\n";
    }
    cout << "\n *** Rozwiązanie dokładne ***\n";
    for (i=1; i <= n; i++) {
        for (j=1; j <= n; j++) { cout.precision(4); cout.width(10); cout << right << u_exact(i*b/(n+1), j*b/(n+1))<< " "; }
        cout << "\n";
    }