add numerical recipes library

lib/nr/ansi/recipes/matsub.c

@@ -0,0 +1,9 @@
+
+void matsub(double **a, double **b, double **c, int n)
+{
+	int i,j;
+
+	for (j=1;j<=n;j++)
+		for (i=1;i<=n;i++)
+			c[i][j]=a[i][j]-b[i][j];
+}