add numerical recipes library

lib/nr/cpp/recipes/rsolv.cpp

@@ -0,0 +1,14 @@
+#include "nr.h"
+
+void NR::rsolv(Mat_I_DP &a, Vec_I_DP &d, Vec_IO_DP &b)
+{
+	int i,j;
+	DP sum;
+
+	int n=a.nrows();
+	b[n-1] /= d[n-1];
+	for (i=n-2;i>=0;i--) {
+		for (sum=0.0,j=i+1;j<n;j++) sum += a[i][j]*b[j];
+		b[i]=(b[i]-sum)/d[i];
+	}
+}