add numerical recipes library

lib/nr/ansi/recipes/slvsm2.c

@@ -0,0 +1,13 @@
+
+#include <math.h>
+
+void slvsm2(double **u, double **rhs)
+{
+	void fill0(double **u, int n);
+	double disc,fact,h=0.5;
+
+	fill0(u,3);
+	fact=2.0/(h*h);
+	disc=sqrt(fact*fact+rhs[2][2]);
+	u[2][2] = -rhs[2][2]/(fact+disc);
+}