add numerical recipes library

lib/nr/cpp/recipes/chixy.cpp

@@ -0,0 +1,30 @@
+#include <cmath>
+#include "nr.h"
+using namespace std;
+
+extern Vec_DP *xx_p,*yy_p,*sx_p,*sy_p,*ww_p;
+extern DP aa,offs;
+
+DP NR::chixy(const DP bang)
+{
+	const DP BIG=1.0e30;
+	int j;
+	DP ans,avex=0.0,avey=0.0,sumw=0.0,b;
+
+	Vec_DP &xx=*xx_p, &yy=*yy_p;
+	Vec_DP &sx=*sx_p, &sy=*sy_p, &ww=*ww_p;
+	int nn=xx.size();
+	b=tan(bang);
+	for (j=0;j<nn;j++) {
+		ww[j] = SQR(b*sx[j])+SQR(sy[j]);
+		sumw += (ww[j]=(ww[j] < 1.0/BIG ? BIG : 1.0/ww[j]));
+		avex += ww[j]*xx[j];
+		avey += ww[j]*yy[j];
+	}
+	avex /= sumw;
+	avey /= sumw;
+	aa=avey-b*avex;
+	for (ans = -offs,j=0;j<nn;j++)
+		ans += ww[j]*SQR(yy[j]-aa-b*xx[j]);
+	return ans;
+}