From 55862aa014f338789aa138831bf778d295c0f3aa Mon Sep 17 00:00:00 2001
From: Saad Jbabdi <saad@fmrib.ox.ac.uk>
Date: Tue, 22 Aug 2006 12:41:27 +0000
Subject: [PATCH] added a permutation function
---
miscprob.cc | 29 +++++++++++++++++++++++++++++
miscprob.h | 3 +++
2 files changed, 32 insertions(+)
diff --git a/miscprob.cc b/miscprob.cc
index 89f7623..00b08a3 100644
--- a/miscprob.cc
+++ b/miscprob.cc
@@ -145,4 +145,33 @@ ReturnMatrix mvnrnd(const RowVector& mu, const SymmetricMatrix& covar, int nsamp
return mvn.next(nsamp);
}
+ReturnMatrix perms(const int n){
+ if(n<=1){
+ Matrix P(1,1);
+ P << n;
+ P.Release();
+ return P;
+ }
+ Matrix Q = perms(n-1); // recursive calls
+ int m = Q.Nrows();
+ Matrix P(n*m,n);
+ for(int i=1;i<=m;i++){
+ P(i,1)=n;
+ for(int j=1;j<=Q.Ncols();j++)
+ P(i,j+1)=Q(i,j);
+ }
+ for(int i=n-1;i>=1;i--){
+ int jj=1;
+ for(int j=(n-i)*m+1;j<=(n-i+1)*m;j++){
+ P(j,1)=i;
+ for(int k=1;k<=n-1;k++){
+ P(j,k+1)= (Q(jj,k)==i) ? n : Q(jj,k);
+ }
+ jj++;
+ }
+ }
+ P.Release();
+ return P;
+}
+
}
diff --git a/miscprob.h b/miscprob.h
index 26c2e04..f0fb80b 100644
--- a/miscprob.h
+++ b/miscprob.h
@@ -41,6 +41,9 @@ namespace MISCMATHS {
ReturnMatrix gammacdf(const RowVector& vals, const float mu = 0, const float var = 1);
+ // returns n! * n matrix of all possible permutations
+ ReturnMatrix perms(const int n);
+
class Mvnormrandm
{
--
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