add numerical recipes library

lib/nr/cpp/recipes/resid.cpp

@@ -0,0 +1,17 @@
+#include "nr.h"
+
+void NR::resid(Mat_O_DP &res, Mat_I_DP &u, Mat_I_DP &rhs)
+{
+	int i,j;
+	DP h,h2i;
+
+	int n=u.nrows();
+	h=1.0/(n-1);
+	h2i=1.0/(h*h);
+	for (j=1;j<n-1;j++)
+		for (i=1;i<n-1;i++)
+			res[i][j] = -h2i*(u[i+1][j]+u[i-1][j]+u[i][j+1]
+				+u[i][j-1]-4.0*u[i][j])+rhs[i][j];
+	for (i=0;i<n;i++)
+		res[i][0]=res[i][n-1]=res[0][i]=res[n-1][i]=0.0;
+}