add numerical recipes library

lib/nr/cpp/recipes/banmul.cpp

@@ -0,0 +1,15 @@
+#include "nr.h"
+
+void NR::banmul(Mat_I_DP &a, const int m1, const int m2, Vec_I_DP &x,
+	Vec_O_DP &b)
+{
+	int i,j,k,tmploop;
+
+	int n=a.nrows();
+	for (i=0;i<n;i++) {
+		k=i-m1;
+		tmploop=MIN(m1+m2+1,int(n-k));
+		b[i]=0.0;
+		for (j=MAX(0,-k);j<tmploop;j++) b[i] += a[i][j]*x[j+k];
+	}
+}