From 3f4f71bf3ca3f504795cfaf1f6be31b1a4df46e9 Mon Sep 17 00:00:00 2001
From: Rowan Cockett <rowan@3ptscience.com>
Date: Mon, 1 Jun 2015 14:01:51 -0700
Subject: [PATCH] reciprocal map

---
 SimPEG/Maps.py            | 20 ++++++++++++++++++++
 SimPEG/Tests/test_maps.py |  4 ++--
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/SimPEG/Maps.py b/SimPEG/Maps.py
index 4ab79e64..4ceb35bd 100644
--- a/SimPEG/Maps.py
+++ b/SimPEG/Maps.py
@@ -221,6 +221,26 @@ class ExpMap(IdentityMap):
         """
         return Utils.sdiag(np.exp(Utils.mkvc(m)))
 
+class ReciprocalMap(IdentityMap):
+    """
+        Reciprocal mapping. For example, electrical resistivity and conductivity.
+
+        .. math::
+
+            \\rho = \\frac{1}{\sigma}
+
+    """
+    def _transform(self, m):
+        return 1.0 / Utils.mkvc(m)
+
+    def inverse(self, D):
+        return 1.0 / Utils.mkvc(m)
+
+    def deriv(self, m):
+        # TODO: if this is a tensor, you might have a problem.
+        return Utils.sdiag( - Utils.mkvc(m)**(-2) )
+
+
 
 class LogMap(IdentityMap):
     """
diff --git a/SimPEG/Tests/test_maps.py b/SimPEG/Tests/test_maps.py
index 9f8fef3c..437e51fa 100644
--- a/SimPEG/Tests/test_maps.py
+++ b/SimPEG/Tests/test_maps.py
@@ -6,8 +6,8 @@ from scipy.sparse.linalg import dsolve
 
 TOL = 1e-14
 
-MAPS_TO_TEST_2D = ["CircleMap", "ComplexMap", "ExpMap", "IdentityMap", "Vertical1DMap", "Weighting"]
-MAPS_TO_TEST_3D = [             "ComplexMap", "ExpMap", "IdentityMap", "Vertical1DMap", "Weighting"]
+MAPS_TO_TEST_2D = ["CircleMap", "ComplexMap", "ExpMap", "IdentityMap", "Vertical1DMap", "Weighting", "ReciprocalMap"]
+MAPS_TO_TEST_3D = [             "ComplexMap", "ExpMap", "IdentityMap", "Vertical1DMap", "Weighting", "ReciprocalMap"]
 
 class MapTests(unittest.TestCase):