From c698b16d75f6ddcee79067c6088b85f87361da1f Mon Sep 17 00:00:00 2001
From: Antonin Portelli <antonin.portelli@me.com>
Date: Sun, 1 May 2016 18:30:35 -0700
Subject: [PATCH] function to generate Chroma-style gamma matrix products

---
 lib/qcd/spin/Dirac.cc | 25 +++++++++++++++++++++++++
 lib/qcd/spin/Dirac.h  |  5 ++++-
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/lib/qcd/spin/Dirac.cc b/lib/qcd/spin/Dirac.cc
index 51c06348..8279a4a7 100644
--- a/lib/qcd/spin/Dirac.cc
+++ b/lib/qcd/spin/Dirac.cc
@@ -60,6 +60,31 @@ namespace Grid {
       "-Gamma5  ",
       "         "
     };
+    
+    SpinMatrix makeGammaProd(const unsigned int i)
+    {
+      SpinMatrix g;
+      
+      g = 1.;
+      if (i & 0x1)
+      {
+        g = g*Gamma(Gamma::GammaMatrix::GammaX);
+      }
+      if (i & 0x2)
+      {
+        g = g*Gamma(Gamma::GammaMatrix::GammaY);
+      }
+      if (i & 0x4)
+      {
+        g = g*Gamma(Gamma::GammaMatrix::GammaZ);
+      }
+      if (i & 0x8)
+      {
+        g = g*Gamma(Gamma::GammaMatrix::GammaT);
+      }
+      
+      return g;
+    }
 
     //    void sprojMul( vHalfSpinColourVector &out,vColourMatrix &u, vSpinColourVector &in){
     //      vHalfSpinColourVector hspin;
diff --git a/lib/qcd/spin/Dirac.h b/lib/qcd/spin/Dirac.h
index 8654b5a8..00bd519c 100644
--- a/lib/qcd/spin/Dirac.h
+++ b/lib/qcd/spin/Dirac.h
@@ -82,7 +82,10 @@ namespace QCD {
     GammaMatrix _g;
 
   };
-
+  
+    // Make gamma products (Chroma convention)
+    SpinMatrix makeGammaProd(const unsigned int i);
+    
     /* Gx
      *  0 0  0  i    
      *  0 0  i  0