1 files changed, 25 insertions, 0 deletions
diff --git a/python_src/xxpp_to_xpxp.py b/python_src/xxpp_to_xpxp.py
new file mode 100644
index 0000000..940d8b8
--- /dev/null
+++ b/python_src/xxpp_to_xpxp.py
@@ -0,0 +1,25 @@
+def xxpp_to_xpxp(S):
+    """Permutes the entries of the input from xxpp ordering to xpxp ordering.
+
+    Args:
+        S (array): input even dimensional square matrix or array
+
+    Returns:
+        (array): permuted matrix or array
+    """
+    shape = S.shape
+    n = shape[0]
+
+    if n % 2 != 0:
+        raise ValueError("The input array is not even-dimensional")
+
+    n = n // 2
+    ind = np.arange(2 * n).reshape(2, -1).T.flatten()
+
+    if len(shape) == 2:
+        if shape[0] != shape[1]:
+            raise ValueError("The input matrix is not square")
+        return S[:, ind][ind]
+
+    return S[ind]
+