add numerical recipes library

lib/nr/k_and_r/recipes/spread.c

@@ -0,0 +1,28 @@
+
+#include "nrutil.h"
+
+void spread(y,yy,n,x,m)
+float x,y,yy[];
+int m;
+unsigned long n;
+{
+	int ihi,ilo,ix,j,nden;
+	static long nfac[11]={0,1,1,2,6,24,120,720,5040,40320,362880};
+	float fac;
+
+	if (m > 10) nrerror("factorial table too small in spread");
+	ix=(int)x;
+	if (x == (float)ix) yy[ix] += y;
+	else {
+		ilo=LMIN(LMAX((long)(x-0.5*m+1.0),1),n-m+1);
+		ihi=ilo+m-1;
+		nden=nfac[m];
+		fac=x-ilo;
+		for (j=ilo+1;j<=ihi;j++) fac *= (x-j);
+		yy[ihi] += y*fac/(nden*(x-ihi));
+		for (j=ihi-1;j>=ilo;j--) {
+			nden=(nden/(j+1-ilo))*(j-ihi);
+			yy[j] += y*fac/(nden*(x-j));
+		}
+	}
+}