void lop(double **out, double **u, int n){	int i,j;	double h,h2i;	h=1.0/(n-1);	h2i=1.0/(h*h);	for (j=2;j<n;j++)		for (i=2;i<n;i++)			out[i][j]=h2i*(u[i+1][j]+u[i-1][j]+u[i][j+1]+u[i][j-1]-				4.0*u[i][j])+u[i][j]*u[i][j];	for (i=1;i<=n;i++)		out[i][1]=out[i][n]=out[1][i]=out[n][i]=0.0;}