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diff --git a/src/mtx_spherical_harmonics/legendre_a.h b/src/mtx_spherical_harmonics/legendre_a.h
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+/* 
+ 
+ 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"
+
+*/
+
+
+#ifndef _legendre_a_h__
+#define _legendre_a_h__
+#include <math.h>
+#include <stdlib.h>
+
+typedef struct _LegendreWorkSpace_
+{
+   size_t nmax;
+   size_t l;
+   double *p;
+} LegendreWorkSpace;
+
+LegendreWorkSpace *legendre_a_alloc(const size_t nmax, const size_t l);
+
+void legendre_a_free(LegendreWorkSpace *wl);
+
+void legendre_a(double *theta, LegendreWorkSpace *wl);
+
+#endif