From 23a3da45293aef5568409c8c1c46fc3b0758ca2d Mon Sep 17 00:00:00 2001
From: Michael Orlitzky <michael@orlitzky.com>
Date: Mon, 25 Feb 2013 10:24:40 -0500
Subject: [PATCH] Add permutation_matrices() and its tests.

---
 permutation_matrices.m             | 31 ++++++++++++++++++++++++++++++
 tests/permutation_matrices_tests.m |  6 ++++++
 2 files changed, 37 insertions(+)
 create mode 100644 permutation_matrices.m
 create mode 100644 tests/permutation_matrices_tests.m

diff --git a/permutation_matrices.m b/permutation_matrices.m
new file mode 100644
index 0000000..9032d2e
--- /dev/null
+++ b/permutation_matrices.m
@@ -0,0 +1,31 @@
+function PMs = permutation_matrices(integerN)
+  ## Generate all permutation matrices of size ``integerN``.
+  ##
+  ## INPUT:
+  ##
+  ##   - ``integerN`` -- The dimension of the resulting matrices.
+  ##
+  ## OUTPUT:
+  ##
+  ##   - ``PMs`` -- A cell array of permutation matrices.
+  ##
+
+  if (integerN < 1)
+    PMs = NA;
+    return;
+  end
+
+  ## Append to this as we generate them.
+  PMs = {};
+
+  ## Generate all permutations of [1,2,...,integerN].
+  permutations = perms([1:integerN]);
+
+  for idx = [ 1 : factorial(integerN) ]
+    sigma = permutations(idx,:);
+    ## Create a permutation matrix from the permutation, sigma.
+    P = eye(integerN) (sigma,:);
+    PMs{end+1} = P;
+  end
+
+end
diff --git a/tests/permutation_matrices_tests.m b/tests/permutation_matrices_tests.m
new file mode 100644
index 0000000..d65049e
--- /dev/null
+++ b/tests/permutation_matrices_tests.m
@@ -0,0 +1,6 @@
+expected = { [1] };
+actual = permutation_matrices(1);
+
+unit_test_equals("permutation_matrices(1) works", ...
+		 true, ...
+		 isequal(actual,expected));
-- 
2.43.2