From c8cb0e4cb81ce28d24973693a96a5db2281a6e28 Mon Sep 17 00:00:00 2001
From: Fabian Joswig <fabian.joswig@ed.ac.uk>
Date: Thu, 23 Dec 2021 12:00:10 +0100
Subject: [PATCH] feat: epsilon tensors moved to dirac submodule, tests added

---
 pyerrors/dirac.py         | 24 ++++++++++++++++++++++++
 pyerrors/input/hadrons.py | 12 ------------
 tests/dirac_test.py       | 12 ++++++++++++
 3 files changed, 36 insertions(+), 12 deletions(-)

diff --git a/pyerrors/dirac.py b/pyerrors/dirac.py
index f5350b94..7f68cb22 100644
--- a/pyerrors/dirac.py
+++ b/pyerrors/dirac.py
@@ -22,6 +22,30 @@ identity = np.array(
     dtype=complex)
 
 
+def epsilon_tensor(i, j, k):
+    """Rank-3 epsilon tensor
+
+    Based on https://codegolf.stackexchange.com/a/160375
+    """
+    test_set = set((i, j, k))
+    if not (test_set <= set((1, 2, 3)) or test_set <= set((0, 1, 2))):
+        raise Exception("Unexpected input", i, j, k)
+
+    return (i - j) * (j - k) * (k - i) / 2
+
+
+def epsilon_tensor_rank4(i, j, k, o):
+    """Rank-4 epsilon tensor
+
+    Extension of https://codegolf.stackexchange.com/a/160375
+    """
+    test_set = set((i, j, k, o))
+    if not (test_set <= set((1, 2, 3, 4)) or test_set <= set((0, 1, 2, 3))):
+        raise Exception("Unexpected input", i, j, k, o)
+
+    return (i - j) * (j - k) * (k - i) * (i - o) * (j - o) * (o - k) / 12
+
+
 def Grid_gamma(gamma_tag):
     """Returns gamma matrix in Grid labeling."""
     if gamma_tag == 'Identity':
diff --git a/pyerrors/input/hadrons.py b/pyerrors/input/hadrons.py
index e139f2b2..efe4feb1 100644
--- a/pyerrors/input/hadrons.py
+++ b/pyerrors/input/hadrons.py
@@ -298,18 +298,6 @@ def read_Fourquark_hd5(path, filestem, ens_id, idl=None, vertices=["VA", "AV"]):
     return result_dict
 
 
-def _epsilon_tensor(i, j, k, o):
-    """Rank-4 epsilon tensor
-
-    Extension of https://codegolf.stackexchange.com/a/160375
-    """
-    test_set = set((i, j, k, o))
-    if not (test_set <= set((1, 2, 3, 4)) or test_set <= set((0, 1, 2, 3))):
-        raise Exception("Unexpected input", i, j, k, o)
-
-    return (i - j) * (j - k) * (k - i) * (i - o) * (j - o) * (o - k) / 12
-
-
 def _get_lorentz_names(name):
     assert len(name) == 2
 
diff --git a/tests/dirac_test.py b/tests/dirac_test.py
index 0a2c0379..f36017a6 100644
--- a/tests/dirac_test.py
+++ b/tests/dirac_test.py
@@ -32,3 +32,15 @@ def test_grid_dirac():
         pe.dirac.Grid_gamma(gamma)
     with pytest.raises(Exception):
         pe.dirac.Grid_gamma('Not a gamma matrix')
+
+
+def test_epsilon_tensor():
+    check = {(1, 2, 3) : 1.0,
+             (3, 1, 2) : 1.0,
+             (2, 3, 1) : 1.0,
+             (1, 1, 1) : 0.0,
+             (3, 2, 1) : -1.0,
+             (1, 3, 2) : -1.0,
+             (1, 1, 3) : 0.0}
+    for key, value in check.items():
+        assert pe.dirac.epsilon_tensor(*key) == value