add numerical recipes library

lib/nr/k_and_r/recipes/matsub.c

@@ -0,0 +1,11 @@
+
+void matsub(a,b,c,n)
+double **a,**b,**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];
+}