From f3fb1e64812c38bf79eba65dd654ba1ed84efae3 Mon Sep 17 00:00:00 2001
From: Lindsey Heagy <lheagy@eos.ubc.ca>
Date: Tue, 24 Nov 2015 10:05:28 -0800
Subject: [PATCH] added an __iadd__, __isub__ to zero class

---
 SimPEG/Utils/matutils.py | 2 ++
 tests/utils/test_Zero.py | 7 +++++++
 2 files changed, 9 insertions(+)

diff --git a/SimPEG/Utils/matutils.py b/SimPEG/Utils/matutils.py
index ee58bf86..b38bb4a1 100644
--- a/SimPEG/Utils/matutils.py
+++ b/SimPEG/Utils/matutils.py
@@ -399,8 +399,10 @@ def diagEst(matFun, n, k=None, approach='Probing'):
 class Zero(object):
     def __add__(self, v):return v
     def __radd__(self, v):return v
+    def __iadd__(self, v):return v
     def __sub__(self, v):return -v
     def __rsub__(self, v):return v
+    def __isub__(self, v):return v
     def __mul__(self, v):return self
     def __rmul__(self, v):return self
     def __div__(self, v): return self
diff --git a/tests/utils/test_Zero.py b/tests/utils/test_Zero.py
index be7c9bbe..594de6a6 100644
--- a/tests/utils/test_Zero.py
+++ b/tests/utils/test_Zero.py
@@ -20,6 +20,13 @@ class Tests(unittest.TestCase):
         assert 3*z == 0
         assert z*3 == 0
         assert z/3 == 0
+
+        a = 1
+        a += z
+        assert a == 1
+        a = 1
+        a += z
+        assert a == 1
         self.assertRaises(ZeroDivisionError, lambda:3/z)
 
     def test_mat_zero(self):