add numerical recipes library

lib/nr/ansi/recipes/rf.c

@@ -0,0 +1,49 @@
+
+#include <math.h>
+#define NRANSI
+#include "nrutil.h"
+#define ERRTOL 0.08
+#define TINY 1.5e-38
+#define BIG 3.0e37
+#define THIRD (1.0/3.0)
+#define C1 (1.0/24.0)
+#define C2 0.1
+#define C3 (3.0/44.0)
+#define C4 (1.0/14.0)
+
+float rf(float x, float y, float z)
+{
+	float alamb,ave,delx,dely,delz,e2,e3,sqrtx,sqrty,sqrtz,xt,yt,zt;
+
+	if (FMIN(FMIN(x,y),z) < 0.0 || FMIN(FMIN(x+y,x+z),y+z) < TINY ||
+		FMAX(FMAX(x,y),z) > BIG)
+			nrerror("invalid arguments in rf");
+	xt=x;
+	yt=y;
+	zt=z;
+	do {
+		sqrtx=sqrt(xt);
+		sqrty=sqrt(yt);
+		sqrtz=sqrt(zt);
+		alamb=sqrtx*(sqrty+sqrtz)+sqrty*sqrtz;
+		xt=0.25*(xt+alamb);
+		yt=0.25*(yt+alamb);
+		zt=0.25*(zt+alamb);
+		ave=THIRD*(xt+yt+zt);
+		delx=(ave-xt)/ave;
+		dely=(ave-yt)/ave;
+		delz=(ave-zt)/ave;
+	} while (FMAX(FMAX(fabs(delx),fabs(dely)),fabs(delz)) > ERRTOL);
+	e2=delx*dely-delz*delz;
+	e3=delx*dely*delz;
+	return (1.0+(C1*e2-C2-C3*e3)*e2+C4*e3)/sqrt(ave);
+}
+#undef ERRTOL
+#undef TINY
+#undef BIG
+#undef THIRD
+#undef C1
+#undef C2
+#undef C3
+#undef C4
+#undef NRANSI