From e099fbf30bb65130d70b19f862e7aaa4360a7eb0 Mon Sep 17 00:00:00 2001
From: Daniel Waggoner <dwaggoner@frbatlanta.org>
Date: Mon, 23 Apr 2012 18:56:24 -0400
Subject: [PATCH] added permutation routine (cherry picked from commit
9db5ba7a4483581a203df01888367897ec4369f9)
---
include/dw_matrix.h | 10 +++++++---
matrix/dw_matrix.c | 33 +++++++++++++++++++++++++++++++++
2 files changed, 40 insertions(+), 3 deletions(-)
diff --git a/include/dw_matrix.h b/include/dw_matrix.h
index 07c7c0f..61a6de2 100644
--- a/include/dw_matrix.h
+++ b/include/dw_matrix.h
@@ -125,19 +125,22 @@
ElementP(x,i) - x : TPermutation
i : int
Returns: L-value int containing the ith element. The index i
- is zero-based. It must be case that
+ is zero-based. It must be case that i < UseP(x) and
- i <= ElementP(x,i) <= DimP(x).
+ i <= ElementP(x,i) < DimP(x).
pElementP(x) - x : TPermutation
Returns: pointer to 0th element of the array storing the
permutation.
-
The representation as a product of transpositions used by TPermutation
(0,ElementP(x,0))*...*(UseP(x)-1,ElementP(x,UseP(x)-1)
+ In order to have a unique representation, we require that
+
+ UseP(x) - 1 < ElementP(x,UseP(x) - 1)
+
*******************************************************************************/
/*******************************************************************************
@@ -552,6 +555,7 @@ TMatrix InMatrix(FILE *f, TMatrix X);
TPermutation CreatePermutation(int m);
void FreePermutation(TPermutation X);
TPermutation InitializePermutation(TPermutation X, int *p, int m);
+int* ExtractPermutation(int *p, TPermutation X);
TPermutation TranspositionPermutation(TPermutation X, int i, int j, int m);
TPermutation EquatePermutation(TPermutation X, TPermutation Y);
TMatrix PermutationMatrix(TMatrix X, TPermutation Y);
diff --git a/matrix/dw_matrix.c b/matrix/dw_matrix.c
index 128fd7e..bb96e93 100644
--- a/matrix/dw_matrix.c
+++ b/matrix/dw_matrix.c
@@ -5251,6 +5251,39 @@ TPermutation InitializePermutation(TPermutation X, int *p, int m)
return X;
}
+/*
+ Assumes:
+ p : integer array of length m or null pointer
+ X : m-permutation
+
+ Results:
+ Allocates the array p if it was null. Fills p with the permutation which
+ maps i to p[i].
+*/
+int* ExtractPermutation(int *p, TPermutation X)
+{
+ int i, j;
+ if (!X)
+ {
+ dw_Error(NULL_ERR);
+ return (int*)NULL;
+ }
+ if (!p && !(p=dw_malloc(DimP(X)*sizeof(int))))
+ {
+ dw_Error(MEM_ERR);
+ return (int*)NULL;
+ }
+ for (i=DimP(X)-1; i >= 0; i--) p[i]=i;
+ for (i=UseP(X)-1; i >= 0; i--)
+ if (X[i] != i)
+ {
+ j=p[i];
+ p[i]=p[X[i]];
+ p[X[i]]=j;
+ }
+ return p;
+}
+
/*
Assumes
X : m-permutation or null pointer
--
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