add numerical recipes library

lib/nr/ansi/recipes/selip.c

@@ -0,0 +1,73 @@
+
+#define NRANSI
+#include "nrutil.h"
+#define M 64
+#define BIG 1.0e30
+#define FREEALL free_vector(sel,1,M+2);free_lvector(isel,1,M+2);
+
+float selip(unsigned long k, unsigned long n, float arr[])
+{
+	void shell(unsigned long n, float a[]);
+	unsigned long i,j,jl,jm,ju,kk,mm,nlo,nxtmm,*isel;
+	float ahi,alo,sum,*sel;
+
+	if (k < 1 || k > n || n <= 0) nrerror("bad input to selip");
+	isel=lvector(1,M+2);
+	sel=vector(1,M+2);
+	kk=k;
+	ahi=BIG;
+	alo = -BIG;
+	for (;;) {
+		mm=nlo=0;
+		sum=0.0;
+		nxtmm=M+1;
+		for (i=1;i<=n;i++) {
+			if (arr[i] >= alo && arr[i] <= ahi) {
+				mm++;
+				if (arr[i] == alo) nlo++;
+				if (mm <= M) sel[mm]=arr[i];
+				else if (mm == nxtmm) {
+					nxtmm=mm+mm/M;
+					sel[1 + ((i+mm+kk) % M)]=arr[i];
+				}
+				sum += arr[i];
+			}
+		}
+		if (kk <= nlo) {
+			FREEALL
+			return alo;
+		}
+		else if (mm <= M) {
+			shell(mm,sel);
+			ahi = sel[kk];
+			FREEALL
+			return ahi;
+		}
+		sel[M+1]=sum/mm;
+		shell(M+1,sel);
+		sel[M+2]=ahi;
+		for (j=1;j<=M+2;j++) isel[j]=0;
+		for (i=1;i<=n;i++) {
+			if (arr[i] >= alo && arr[i] <= ahi) {
+				jl=0;
+				ju=M+2;
+				while (ju-jl > 1) {
+					jm=(ju+jl)/2;
+					if (arr[i] >= sel[jm]) jl=jm;
+					else ju=jm;
+				}
+				isel[ju]++;
+			}
+		}
+		j=1;
+		while (kk > isel[j]) {
+			alo=sel[j];
+			kk -= isel[j++];
+		}
+		ahi=sel[j];
+	}
+}
+#undef M
+#undef BIG
+#undef FREEALL
+#undef NRANSI