--- branches/development/src/math/SquareMatrix.hpp	2011/11/22 20:38:56	1665
+++ branches/development/src/math/SquareMatrix.hpp	2012/06/21 19:26:46	1760
@@ -133,9 +133,28 @@ namespace OpenMD {
       for (unsigned int i = 0; i < Dim ; i++)
 	tmp += this->data_[i][i];
 
+      return tmp;
+    }
+    
+    /**
+     * Returns the tensor contraction (double dot product) of two rank 2
+     * tensors (or Matrices)
+     * @param t1 first tensor
+     * @param t2 second tensor
+     * @return the tensor contraction (double dot product) of t1 and t2
+     */
+    Real doubleDot( const SquareMatrix<Real, Dim>& t1, const SquareMatrix<Real, Dim>& t2 ) {
+      Real tmp;
+      tmp = 0;
+      
+      for (unsigned int i = 0; i < Dim; i++)
+        for (unsigned int j =0; j < Dim; j++)
+          tmp += t1[i][j] * t2[i][j];
+      
       return tmp;
     }
 
+
     /** Tests if this matrix is symmetrix. */            
     bool isSymmetric() const {
       for (unsigned int i = 0; i < Dim - 1; i++)
@@ -165,6 +184,19 @@ namespace OpenMD {
       return true;
     }
 
+    /** 
+     * Returns a column vector that contains the elements from the
+     * diagonal of m in the order R(0) = m(0,0), R(1) = m(1,1), and so
+     * on.
+     */
+    Vector<Real, Dim> diagonals() const {
+      Vector<Real, Dim> result;
+      for (unsigned int i = 0; i < Dim; i++) {
+        result(i) = this->data_[i][i];
+      }
+      return result;
+    }
+
     /** Tests if this matrix is the unit matrix. */
     bool isUnitMatrix() const {
       if (!isDiagonal())