add numerical recipes library

lib/nr/cpp/recipes/revcst.cpp

@@ -0,0 +1,31 @@
+#include <cmath>
+#include "nr.h"
+using namespace std;
+
+namespace {
+	inline DP alen(const DP a, const DP b, const DP c, const DP d)
+	{
+		return sqrt((b-a)*(b-a)+(d-c)*(d-c));
+	}
+}
+
+DP NR::revcst(Vec_I_DP &x, Vec_I_DP &y, Vec_I_INT &iorder, Vec_IO_INT &n)
+{
+	int j,ii;
+	DP de;
+	Vec_DP xx(4),yy(4);
+
+	int ncity=x.size();
+	n[2]=(n[0]+ncity-1) % ncity;
+	n[3]=(n[1]+1) % ncity;
+	for (j=0;j<4;j++) {
+		ii=iorder[n[j]];
+		xx[j]=x[ii];
+		yy[j]=y[ii];
+	}
+	de = -alen(xx[0],xx[2],yy[0],yy[2]);
+	de -= alen(xx[1],xx[3],yy[1],yy[3]);
+	de += alen(xx[0],xx[3],yy[0],yy[3]);
+	de += alen(xx[1],xx[2],yy[1],yy[2]);
+	return de;
+}