add numerical recipes library

2025-09-12 18:55:25 +09:00
parent d4dff245bd
commit 2c75620ec9
1344 changed files with 63869 additions and 0 deletions
--- a/lib/nr/cpp/recipes/dawson.cpp
+++ b/lib/nr/cpp/recipes/dawson.cpp
@@ -0,0 +1,35 @@
+#include <cmath>
+#include "nr.h"
+using namespace std;
+
+DP NR::dawson(const DP x)
+{
+	const int NMAX=6;
+	const DP H=0.4, A1=2.0/3.0, A2=0.4, A3=2.0/7.0;
+	int i,n0;
+	static bool init = true;
+	DP d1,d2,e1,e2,sum,x2,xp,xx,ans;
+	static Vec_DP c(NMAX);
+
+	if (init) {
+		init=false;
+		for (i=0;i<NMAX;i++) c[i]=exp(-SQR((2.0*i+1.0)*H));
+	}
+	if (fabs(x) < 0.2) {
+		x2=x*x;
+		ans=x*(1.0-A1*x2*(1.0-A2*x2*(1.0-A3*x2)));
+	} else {
+		xx=fabs(x);
+		n0=2*int(0.5*xx/H+0.5);
+		xp=xx-n0*H;
+		e1=exp(2.0*xp*H);
+		e2=e1*e1;
+		d1=n0+1;
+		d2=d1-2.0;
+		sum=0.0;
+		for (i=0;i<NMAX;i++,d1+=2.0,d2-=2.0,e1*=e2)
+			sum += c[i]*(e1/d1+1.0/(d2*e1));
+		ans=0.5641895835*SIGN(exp(-xp*xp),x)*sum;
+	}
+	return ans;
+}