From fb5779b24b2a3302fe1b6adb946d300d1a407674 Mon Sep 17 00:00:00 2001
From: Saad Jbabdi <saad@fmrib.ox.ac.uk>
Date: Tue, 3 Jul 2007 08:53:53 +0000
Subject: [PATCH] added sampling from a distribution given a histogram
---
miscprob.cc | 20 ++++++++++++++++++++
miscprob.h | 2 ++
2 files changed, 22 insertions(+)
diff --git a/miscprob.cc b/miscprob.cc
index 37396b1..830424d 100644
--- a/miscprob.cc
+++ b/miscprob.cc
@@ -36,6 +36,26 @@ ReturnMatrix unifrnd(const int dim1, const int dim2, const float start, const fl
return res;
}
+ // SJ. Generates a sample from a distribution given the histogram
+int distribrnd(const ColumnVector& histo){
+ int res=1;
+ ColumnVector cumsum(histo.Nrows());
+ float sum=0.0;
+ for(int k=1;k<=histo.Nrows();k++){
+ sum += histo(k);
+ cumsum(k) = sum;
+ }
+ float U=rand()/float(RAND_MAX);
+ U *= sum;
+ for(int k=1;k<=histo.Nrows();k++){
+ if(U<cumsum(k)){
+ res = k;
+ break;
+ }
+ }
+ return res;
+}
+
ReturnMatrix normrnd(const int dim1, const int dim2, const float mu, const float sigma)
{
int tdim = dim2;
diff --git a/miscprob.h b/miscprob.h
index 879186a..44099c9 100644
--- a/miscprob.h
+++ b/miscprob.h
@@ -23,6 +23,8 @@ namespace MISCMATHS {
ReturnMatrix unifrnd(const int dim1 = 1, const int dim2 = -1,
const float start = 0, const float end = 1);
+
+ int distribrnd(const ColumnVector& histo);
ReturnMatrix normrnd(const int dim1 = 1, const int dim2 = -1,
const float mu = 0, const float sigma = 1);
--
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