add numerical recipes library

lib/nr/k_and_r/recipes/sinft.c

@@ -0,0 +1,34 @@
+
+#include <math.h>
+
+void sinft(y,n)
+float y[];
+int n;
+{
+	void realft();
+	int j,n2=n+2;
+	float sum,y1,y2;
+	double theta,wi=0.0,wr=1.0,wpi,wpr,wtemp;
+
+	theta=3.14159265358979/(double) n;
+	wtemp=sin(0.5*theta);
+	wpr = -2.0*wtemp*wtemp;
+	wpi=sin(theta);
+	y[1]=0.0;
+	for (j=2;j<=(n>>1)+1;j++) {
+		wr=(wtemp=wr)*wpr-wi*wpi+wr;
+		wi=wi*wpr+wtemp*wpi+wi;
+		y1=wi*(y[j]+y[n2-j]);
+		y2=0.5*(y[j]-y[n2-j]);
+		y[j]=y1+y2;
+		y[n2-j]=y1-y2;
+	}
+	realft(y,n,1);
+	y[1]*=0.5;
+	sum=y[2]=0.0;
+	for (j=1;j<=n-1;j+=2) {
+		sum += y[j];
+		y[j]=y[j+1];
+		y[j+1]=sum;
+	}
+}