From 1e331f2c504ed39acae933d04828e8626363b35b Mon Sep 17 00:00:00 2001
From: Philipp Arras <parras@mpa-garching.mpg.de>
Date: Tue, 30 Jan 2018 21:21:02 +0100
Subject: [PATCH] Add comment on missing curvature tests

---
 test/test_energies/test_map.py   | 4 ++++
 test/test_energies/test_power.py | 4 ++++
 2 files changed, 8 insertions(+)

diff --git a/test/test_energies/test_map.py b/test/test_energies/test_map.py
index dfa0f81e7..bac03da22 100644
--- a/test/test_energies/test_map.py
+++ b/test/test_energies/test_map.py
@@ -158,6 +158,10 @@ class Energy_Tests(unittest.TestCase):
 
 
 class Curvature_Tests(unittest.TestCase):
+    # Note: It is only possible to test linear curvatures since the non-linear
+    # curvatures are not the exact second derivative but only a part of it. One
+    # term is neglected which would render the second derivative non-positive
+    # definite.
     @expand(product([ift.RGSpace(64, distances=.789),
                      ift.RGSpace([32, 32], distances=.789)],
                     [4, 78, 23]))
diff --git a/test/test_energies/test_power.py b/test/test_energies/test_power.py
index 743b7281c..74c979322 100644
--- a/test/test_energies/test_power.py
+++ b/test/test_energies/test_power.py
@@ -146,6 +146,10 @@ class Energy_Tests(unittest.TestCase):
 
 
 class Curvature_Tests(unittest.TestCase):
+    # Note: It is only possible to test the linear power curvatures since the
+    # non-linear curvatures are not the exact second derivative but only a part
+    # of it. One term is neglected which would render the second derivative
+    # non-positive definite.
     @expand(product([ift.RGSpace(64, distances=.789),
                      ift.RGSpace([32, 32], distances=.789)],
                     [132, 42, 3]))
-- 
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