From 6187aede8dc13a4fc4d5fd5463574955d702d7f4 Mon Sep 17 00:00:00 2001
From: "Eugeniy E. Mikhailov" <evgmik@gmail.com>
Date: Tue, 19 Nov 2024 13:00:14 -0500
Subject: initial release

---
 xpxp_to_xxpp.m | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)
 create mode 100644 xpxp_to_xxpp.m

(limited to 'xpxp_to_xxpp.m')

diff --git a/xpxp_to_xxpp.m b/xpxp_to_xxpp.m
new file mode 100644
index 0000000..fc732e2
--- /dev/null
+++ b/xpxp_to_xxpp.m
@@ -0,0 +1,32 @@
+function S_permuted = xpxp_to_xxpp(S)
+    % Permutes the entries of the input from xpxp ordering to xxpp ordering.
+    %
+    % Args:
+    %   S (array): input even dimensional square matrix or a row vector
+    %
+    % Returns:
+    %   S_permuted (array): permuted matrix or vector
+
+    shape = size(S);
+    if length(shape) > 2
+        error('The input matrix is not 2 dimensional');
+    end
+
+    n = shape(2);
+
+    if mod(n, 2) ~= 0
+        error('The input array is not even-dimensional');
+    end
+
+    n = n / 2;
+    ind = reshape(1:2*n, 2, [])';
+    ind = ind(:)';
+
+    
+    if shape(1) == shape(2)
+        S_permuted = S(ind, ind);
+    else
+        S_permuted = S(ind);
+    end
+end
+
-- 
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