From 056dc09fa63a3cc0e6582a915b5605f1f4206338 Mon Sep 17 00:00:00 2001
From: D Fournier <fourndo@gmail.com>
Date: Fri, 29 Apr 2016 15:10:30 -0700
Subject: [PATCH] Fix Update_Precondition directive

---
 SimPEG/Directives.py | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/SimPEG/Directives.py b/SimPEG/Directives.py
index ee29e770..b32cd798 100644
--- a/SimPEG/Directives.py
+++ b/SimPEG/Directives.py
@@ -305,11 +305,24 @@ class Update_IRLS(InversionDirective):
         self.reg._W = None
 
 class Update_lin_PreCond(InversionDirective):
-
-
+    """
+    Create a Jacobi preconditioner for the linear problem
+    """
+    onlyOnStart=True
+    
+    def initialize(self):
+    
+        if getattr(self.opt, 'approxHinv', None) is None:
+            # Update the pre-conditioner
+            diagA = np.sum(self.prob.G**2.,axis=0) + self.invProb.beta*(self.reg.W.T*self.reg.W).diagonal() #* (self.reg.mapping * np.ones(self.reg.curModel.size))**2.
+            PC     = Utils.sdiag(diagA**-1.)
+            self.opt.approxHinv = PC
+            
     def endIter(self):
         # Cool the threshold parameter
-
+        if self.onlyOnStart==True:
+            return
+            
         if getattr(self.opt, 'approxHinv', None) is not None:
             # Update the pre-conditioner
             diagA = np.sum(self.prob.G**2.,axis=0) + self.invProb.beta*(self.reg.W.T*self.reg.W).diagonal() #* (self.reg.mapping * np.ones(self.reg.curModel.size))**2.