add numerical recipes library

lib/nr/cpp/recipes/bandec.cpp

@@ -0,0 +1,45 @@
+#include <cmath>
+#include "nr.h"
+using namespace std;
+
+void NR::bandec(Mat_IO_DP &a, const int m1, const int m2, Mat_O_DP &al,
+	Vec_O_INT &indx, DP &d)
+{
+	const DP TINY=1.0e-20;
+	int i,j,k,l,mm;
+	DP dum;
+
+	int n=a.nrows();
+	mm=m1+m2+1;
+	l=m1;
+	for (i=0;i<m1;i++) {
+		for (j=m1-i;j<mm;j++) a[i][j-l]=a[i][j];
+		l--;
+		for (j=mm-l-1;j<mm;j++) a[i][j]=0.0;
+	}
+	d=1.0;
+	l=m1;
+	for (k=0;k<n;k++) {
+		dum=a[k][0];
+		i=k;
+		if (l<n) l++;
+		for (j=k+1;j<l;j++) {
+			if (fabs(a[j][0]) > fabs(dum)) {
+				dum=a[j][0];
+				i=j;
+			}
+		}
+		indx[k]=i+1;
+		if (dum == 0.0) a[k][0]=TINY;
+		if (i != k) {
+			d = -d;
+			for (j=0;j<mm;j++) SWAP(a[k][j],a[i][j]);
+		}
+		for (i=k+1;i<l;i++) {
+			dum=a[i][0]/a[k][0];
+			al[k][i-k-1]=dum;
+			for (j=1;j<mm;j++) a[i][j-1]=a[i][j]-dum*a[k][j];
+			a[i][mm-1]=0.0;
+		}
+	}
+}