add numerical recipes library

lib/nr/ansi/recipes/lop.c

@@ -0,0 +1,15 @@
+
+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;
+}