From 92b9deaf8d7c2a96c3977e1204341d6b6feb1fc1 Mon Sep 17 00:00:00 2001
From: Franz Zotter <fzotter@users.sourceforge.net>
Date: Wed, 14 Jan 2009 10:58:32 +0000
Subject: renamed [mtx_sh] to [mtx_spherical_harmonics].

svn path=/trunk/externals/iem/iemmatrix/; revision=10549
---
 src/mtx_spherical_harmonics/legendre_a.c | 120 +++++++++++++++++++++++++++++++
 1 file changed, 120 insertions(+)
 create mode 100644 src/mtx_spherical_harmonics/legendre_a.c

(limited to 'src/mtx_spherical_harmonics/legendre_a.c')

diff --git a/src/mtx_spherical_harmonics/legendre_a.c b/src/mtx_spherical_harmonics/legendre_a.c
new file mode 100644
index 0000000..a0762b1
--- /dev/null
+++ b/src/mtx_spherical_harmonics/legendre_a.c
@@ -0,0 +1,120 @@
+/* 
+ 
+ Evaluates all associated legendre functions 
+ at the angles theta up to the order nmax
+ using the three-term recurrence of the Legendre functions.
+ P has dimensions length(theta) x (nmax+1)(nmax+2)
+
+ Implementation by Franz Zotter, Institute of Electronic Music and Acoustics
+ (IEM), University of Music and Dramatic Arts (KUG), Graz, Austria
+ http://iem.at/Members/zotter, 2008.
+
+ This code is published under the Gnu General Public License, see
+ "LICENSE.txt"
+
+*/
+
+#include "mtx_spherical_harmonics/legendre_a.h"
+
+static void legendre_first_recurrence (double *sintheta, LegendreWorkSpace *wl) {
+   int n,l,l0;
+   int nmo0=0;
+   int n0=1;
+   const int incr=(wl->nmax+1)*(wl->nmax+2)/2;
+
+   // computes the legendre functions P_n^m(costheta) for m=n
+   // from P_0^0
+   for (n=1; n<=wl->nmax; n++) {
+      for (l=0,l0=0; l<wl->l; l++,l0+=incr) {
+         wl->p[l0+n0+n] = -(2*n-1) * wl->p[l0+nmo0+n-1] * sintheta[l];
+      }
+      nmo0=n0;
+      n0+=n+1;
+   }
+}
+
+static void legendre_second_recurrence (double *costheta, LegendreWorkSpace *wl) {
+   int m,n,l,l0;
+   int nmt0=-1;
+   int nmo0=0;
+   int n0=1;
+   const int incr=(wl->nmax+1)*(wl->nmax+2)/2;
+
+   // computes the Legendre functions P_n^m(costheta) from
+   // P_n^m with m=n
+   for (n=1; n<=wl->nmax; n++) {
+      for (m=0; m<n; m++) {
+	 if (m<=n-2) {
+	    for (l=0,l0=0; l<wl->l; l++,l0+=incr) {
+	       wl->p[l0+n0+m] = (
+		     (2*n-1) * costheta[l] * wl->p[l0+nmo0+m]
+		     - (n+m-1) * wl->p[l0+nmt0+m]
+		     ) / (n-m);
+	    }
+	 }
+	 else {
+	    for (l=0,l0=0; l<wl->l; l++,l0+=incr) {
+	       wl->p[l0+n0+m] = (
+		     (2*n-1) * costheta[l] * wl->p[l0+nmo0+m]
+		     ) / (n-m);
+	    }
+	 }
+      }
+      nmt0=nmo0;
+      nmo0=n0;
+      n0+=n+1;
+   }
+}
+
+LegendreWorkSpace *legendre_a_alloc(const size_t nmax, const size_t l) {
+   LegendreWorkSpace *wl;
+   // memory allocation
+   if ((wl=(LegendreWorkSpace*)calloc(1,sizeof(LegendreWorkSpace)))!=0) {
+      wl->l=l;
+      wl->nmax=nmax;
+      if ((wl->p=(double*)calloc(l*(nmax+1)*(nmax+2)/2,sizeof(double)))==0) {
+         free(wl);
+         wl = 0;
+      }
+   }
+   return wl;
+}
+
+void legendre_a_free(LegendreWorkSpace *wl) {
+   if (wl!=0) {
+      free(wl->p);
+      free(wl);
+   }
+}
+
+void legendre_a(double *theta, LegendreWorkSpace *wl) {
+   int l,l0;
+   const int incr=(wl->nmax+1)*(wl->nmax+2)/2;
+   double *costheta;
+   double *sintheta;
+   
+   // memory allocation
+   if ((wl!=0)&&(theta!=0)) {
+      if ((costheta=(double*)calloc(wl->l,sizeof(double)))==0) {
+         return;
+      }
+      if ((sintheta=(double*)calloc(wl->l,sizeof(double)))==0) {
+         free(costheta);
+         return;
+      }
+      // constants and initialization
+      for (l=0, l0=0; l<wl->l; l++, l0+=incr) {
+         costheta[l]=cos(theta[l]);
+         sintheta[l]=sin(theta[l]);
+         // initial value P_0^0=1
+         wl->p[l0]=1;
+      }
+      // recurrences evaluating all the Legendre functions
+      legendre_first_recurrence(sintheta,wl);
+      legendre_second_recurrence(costheta,wl);
+      free(sintheta);
+      free(costheta);
+   }
+}
+
+
-- 
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