From 0f85b086931cd286abc850ad4ee1e3eb6075f528 Mon Sep 17 00:00:00 2001
From: Olivier Parcollet <olivier.parcollet@cea.fr>
Date: Sun, 12 Jan 2014 20:46:10 +0100
Subject: [PATCH] add trace for ImmutableMatrix

---
 triqs/arrays/matrix.hpp | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/triqs/arrays/matrix.hpp b/triqs/arrays/matrix.hpp
index 1562ef3d..0b50b15b 100644
--- a/triqs/arrays/matrix.hpp
+++ b/triqs/arrays/matrix.hpp
@@ -222,6 +222,16 @@ namespace triqs { namespace arrays {
    return a;
   }
 
+  template <typename M>
+  TYPE_ENABLE_IF(typename M::value_type, ImmutableMatrix<M>) trace(M const &m) {
+    auto r = typename M::value_type{};
+    if (first_dim(m) != second_dim(m))
+      TRIQS_RUNTIME_ERROR << " Trace of a non square matrix";
+    auto d = first_dim(m);
+    for (int i = 0; i < d; ++i)
+      r += m(i, i);
+    return r;
+  }
 }}//namespace triqs::arrays
 
 // The std::swap is WRONG for a view because of the copy/move semantics of view.