add numerical recipes library

lib/nr/cpp/recipes/wtn.cpp

@@ -0,0 +1,31 @@
+#include "nr.h"
+
+void NR::wtn(Vec_IO_DP &a, Vec_I_INT &nn, const int isign,
+	void wtstep(Vec_IO_DP &, const int, const int))
+{
+	int idim,i1,i2,i3,k,n,nnew,nprev=1,nt,ntot=1;
+
+	int ndim=nn.size();
+	for (idim=0;idim<ndim;idim++) ntot *= nn[idim];
+	for (idim=0;idim<ndim;idim++) {
+		n=nn[idim];
+		Vec_DP wksp(n);
+		nnew=n*nprev;
+		if (n > 4) {
+			for (i2=0;i2<ntot;i2+=nnew) {
+				for (i1=0;i1<nprev;i1++) {
+					for (i3=i1+i2,k=0;k<n;k++,i3+=nprev) wksp[k]=a[i3];
+					if (isign >= 0) {
+						for(nt=n;nt>=4;nt >>= 1)
+							wtstep(wksp,nt,isign);
+					} else {
+						for(nt=4;nt<=n;nt <<= 1)
+							wtstep(wksp,nt,isign);
+					}
+					for (i3=i1+i2,k=0;k<n;k++,i3+=nprev) a[i3]=wksp[k];
+				}
+			}
+		}
+		nprev=nnew;
+	}
+}