From 09e5cdc0dd3991e69982bce6872edf201f25e7ed Mon Sep 17 00:00:00 2001
From: Joseph Rushton Wakeling <joe@webdrake.net>
Date: Mon, 10 May 2010 09:13:10 +0200
Subject: [PATCH] Flat (uniform) distribution over open interval.

* Two new functions that provide random variates and the
  pdf of a flat (uniform) distribution over the open
  interval (a, b).

* Corrected a potentially misleading comment in the
  function for a uniform distribution on the half-closed
  interval [a, b).
---
 randist/flat.c        |   33 ++++++++++++++++++++++++++++++++-
 randist/gsl_randist.h |    2 ++
 2 files changed, 34 insertions(+), 1 deletions(-)

diff --git a/randist/flat.c b/randist/flat.c
index 996366e..0a72a85 100644
--- a/randist/flat.c
+++ b/randist/flat.c
@@ -34,7 +34,7 @@ gsl_ran_flat (const gsl_rng * r, const double a, const double b)
 {
   double u = gsl_rng_uniform (r);
 
-  /* A uniform distribution over [a,b] */
+  /* A uniform distribution over the half-open interval [a,b) */
 
   return a * (1 - u) + b * u;
 }
@@ -51,3 +51,34 @@ gsl_ran_flat_pdf (double x, const double a, const double b)
       return 0;
     }
 }
+
+
+/* This is the uniform distribution in the range (a, b)
+
+   p(x) dx = 1/(b-a) dx   if  a < x < b
+   .....   = 0            otherwise
+
+ */
+
+double
+gsl_ran_flat_open (const gsl_rng *r, const double a, const double b)
+{
+  double u = gsl_rng_uniform_pos (r);
+
+  /* A uniform distribution over the open interval (a, b) */
+
+  return a * (1 - u) + b * u;
+}
+
+double
+gsl_ran_flat_open_pdf (double x, const double a, const double b)
+{
+  if (x < b && x > a)
+    {
+      return 1 / (b - a);
+    }
+  else
+    {
+      return 0;
+    }
+}
diff --git a/randist/gsl_randist.h b/randist/gsl_randist.h
index 6f4b0e3..7218c76 100644
--- a/randist/gsl_randist.h
+++ b/randist/gsl_randist.h
@@ -68,6 +68,8 @@ double gsl_ran_fdist_pdf (const double x, const double nu1, const double nu2);
 
 double gsl_ran_flat (const gsl_rng * r, const double a, const double b);
 double gsl_ran_flat_pdf (double x, const double a, const double b);
+double gsl_ran_flat_open (const gsl_rng * r, const double a, const double b);
+double gsl_ran_flat_open_pdf (double x, const double a, const double b);
 
 double gsl_ran_gamma (const gsl_rng * r, const double a, const double b);
 double gsl_ran_gamma_int (const gsl_rng * r, const unsigned int a);
-- 
1.7.0.4