add numerical recipes library

lib/nr/cpp/recipes/banbks.cpp

@@ -0,0 +1,25 @@
+#include "nr.h"
+
+void NR::banbks(Mat_I_DP &a, const int m1, const int m2, Mat_I_DP &al,
+	Vec_I_INT &indx, Vec_IO_DP &b)
+{
+	int i,j,k,l,mm;
+	DP dum;
+
+	int n=a.nrows();
+	mm=m1+m2+1;
+	l=m1;
+	for (k=0;k<n;k++) {
+		j=indx[k]-1;
+		if (j!=k) SWAP(b[k],b[j]);
+		if (l<n) l++;
+		for (j=k+1;j<l;j++) b[j] -= al[k][j-k-1]*b[k];
+	}
+	l=1;
+	for (i=n-1;i>=0;i--) {
+		dum=b[i];
+		for (k=1;k<l;k++) dum -= a[i][k]*b[k+i];
+		b[i]=dum/a[i][0];
+		if (l<mm) l++;
+	}
+}