From b712756e74e3e3c101064bbefc1d062b73d11443 Mon Sep 17 00:00:00 2001
From: Arun Isaac
Date: Tue, 23 Feb 2021 16:29:44 +0530
Subject: Implement the lower incomplete gamma function as a scheme wrapper.

With this change, the wrapper around the gsl lower incomplete gamma
function is directly in scheme. Earlier, there was one layer of
wrapping in C which needed to be wrapped again in scheme.

* include/utils.h (lower_incomplete_gamma): Delete function.
* src/utils.sc (lower-incomplete-gamma): Delete function.
* scm/extent-sampling/wrap.scm (lower-incomplete-gamma): New function.
---
 include/utils.h              |  1 -
 scm/extent-sampling/wrap.scm | 10 ++++++++++
 src/utils.sc                 |  4 ----
 3 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/include/utils.h b/include/utils.h
index e28ee91..5cec86c 100644
--- a/include/utils.h
+++ b/include/utils.h
@@ -10,7 +10,6 @@ double volume_of_ball (unsigned int dimension);
 double ln_volume_of_ball (unsigned int dimension);
 double surface_area_of_ball (unsigned int dimension);
 double ln_surface_area_of_ball (unsigned int dimension);
-double lower_incomplete_gamma (double s, double x);
 
 double angle_between_vectors (const gsl_vector* x, const gsl_vector* y);
 double dot_product (const gsl_vector* x, const gsl_vector* y);
diff --git a/scm/extent-sampling/wrap.scm b/scm/extent-sampling/wrap.scm
index 65fd7ad..0e32452 100644
--- a/scm/extent-sampling/wrap.scm
+++ b/scm/extent-sampling/wrap.scm
@@ -30,6 +30,16 @@
                       (dynamic-func "surface_area_of_ball" lib-extentsampling)
                       (list int)))
 
+(define-public (lower-incomplete-gamma s x)
+  (* ((pointer->procedure double
+                          (dynamic-func "gsl_sf_gamma" lib-gsl)
+                          (list double))
+      s)
+     ((pointer->procedure double
+                          (dynamic-func "gsl_sf_gamma_inc_P" lib-gsl)
+                          (list double double))
+      s x)))
+
 (define-public angle-between-vectors
   (pointer->procedure double
                       (dynamic-func "angle_between_vectors" lib-extentsampling)
diff --git a/src/utils.sc b/src/utils.sc
index a481109..3d96b40 100644
--- a/src/utils.sc
+++ b/src/utils.sc
@@ -39,10 +39,6 @@ sphere, etc."
 2 corresponds to a circle, 3 corresponds to a sphere, etc."
   (return (* dimension (volume-of-ball dimension))))
 
-(define (lower-incomplete-gamma s x) (double double double)
-  (return (* (gsl-sf-gamma s)
-             (gsl-sf-gamma-inc-P s x))))
-
 (define (angle-between-vectors x y) (double (const gsl-vector*) (const gsl-vector*))
   "Return the angle between vectors X and Y. The returned value is in
 the range [0,pi]."
-- 
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