give Zero a transpose

SimPEG/Utils/matutils.py

@@ -26,6 +26,9 @@ def mkvc(x, numDims=1):
     if hasattr(x, 'tovec'):
         x = x.tovec()
 
+    if isinstance(x, Zero):
+        return x
+    
     assert isinstance(x, np.ndarray), "Vector must be a numpy array"
 
     if numDims == 1:
@@ -37,6 +40,9 @@ def mkvc(x, numDims=1):
 
 def sdiag(h):
     """Sparse diagonal matrix"""
+    if isinstance(h, Zero):
+        return h
+
     return sp.spdiags(mkvc(h), 0, h.size, h.size, format="csr")
 
 def sdInv(M):
@@ -417,6 +423,12 @@ class Zero(object):
     def __ge__(self, v):return 0 >= v
     def __gt__(self, v):return 0 > v
 
+    @property 
+    def transpose(self): return Zero()
+    
+    @property
+    def T(self): return Zero()
+
 class Identity(object):
     _positive = True
     def __init__(self, positive=True):

tests/utils/test_Zero.py

@@ -1,5 +1,5 @@
 import unittest
-from SimPEG.Utils import Zero, Identity, sdiag
+from SimPEG.Utils import Zero, Identity, sdiag, mkvc
 from SimPEG import np, sp
 
 class Tests(unittest.TestCase):
@@ -29,6 +29,11 @@ class Tests(unittest.TestCase):
         assert a == 1
         self.assertRaises(ZeroDivisionError, lambda:3/z)
 
+        assert mkvc(z) == 0
+        assert sdiag(z)*a == 0
+        assert z.T == 0
+        assert z.transpose == 0
+
     def test_mat_zero(self):
         z = Zero()
         S = sdiag(np.r_[2,3])