add numerical recipes library

lib/nr/k_and_r/recipes/rzextr.c

@@ -0,0 +1,45 @@
+
+#include "nrutil.h"
+
+extern float **d,*x;
+
+void rzextr(iest,xest,yest,yz,dy,nv)
+float dy[],xest,yest[],yz[];
+int iest,nv;
+{
+	int k,j;
+	float yy,v,ddy,c,b1,b,*fx;
+
+	fx=vector(1,iest);
+	x[iest]=xest;
+	if (iest == 1)
+		for (j=1;j<=nv;j++) {
+			yz[j]=yest[j];
+			d[j][1]=yest[j];
+			dy[j]=yest[j];
+		}
+	else {
+		for (k=1;k<iest;k++)
+			fx[k+1]=x[iest-k]/xest;
+		for (j=1;j<=nv;j++) {
+			v=d[j][1];
+			d[j][1]=yy=c=yest[j];
+			for (k=2;k<=iest;k++) {
+				b1=fx[k]*v;
+				b=b1-c;
+				if (b) {
+					b=(c-v)/b;
+					ddy=c*b;
+					c=b1*b;
+				} else
+					ddy=v;
+				if (k != iest) v=d[j][k];
+				d[j][k]=ddy;
+				yy += ddy;
+			}
+			dy[j]=ddy;
+			yz[j]=yy;
+		}
+	}
+	free_vector(fx,1,iest);
+}