add numerical recipes library

lib/nr/k_and_r/recipes/drealft.c

@@ -0,0 +1,49 @@
+
+#include <math.h>
+
+void drealft(data,n,isign)
+double data[];
+int isign;
+unsigned long n;
+{
+	void dfour1();
+	unsigned long i,i1,i2,i3,i4,np3;
+	double c1=0.5,c2,h1r,h1i,h2r,h2i;
+	double wr,wi,wpr,wpi,wtemp,theta;
+
+	theta=3.141592653589793/(double) (n>>1);
+	if (isign == 1) {
+		c2 = -0.5;
+		dfour1(data,n>>1,1);
+	} else {
+		c2=0.5;
+		theta = -theta;
+	}
+	wtemp=sin(0.5*theta);
+	wpr = -2.0*wtemp*wtemp;
+	wpi=sin(theta);
+	wr=1.0+wpr;
+	wi=wpi;
+	np3=n+3;
+	for (i=2;i<=(n>>2);i++) {
+		i4=1+(i3=np3-(i2=1+(i1=i+i-1)));
+		h1r=c1*(data[i1]+data[i3]);
+		h1i=c1*(data[i2]-data[i4]);
+		h2r = -c2*(data[i2]+data[i4]);
+		h2i=c2*(data[i1]-data[i3]);
+		data[i1]=h1r+wr*h2r-wi*h2i;
+		data[i2]=h1i+wr*h2i+wi*h2r;
+		data[i3]=h1r-wr*h2r+wi*h2i;
+		data[i4] = -h1i+wr*h2i+wi*h2r;
+		wr=(wtemp=wr)*wpr-wi*wpi+wr;
+		wi=wi*wpr+wtemp*wpi+wi;
+	}
+	if (isign == 1) {
+		data[1] = (h1r=data[1])+data[2];
+		data[2] = h1r-data[2];
+	} else {
+		data[1]=c1*((h1r=data[1])+data[2]);
+		data[2]=c1*(h1r-data[2]);
+		dfour1(data,n>>1,-1);
+	}
+}