ENH: add identity matrix constructor to RectangularMatrix

src/OpenFOAM/matrices/RectangularMatrix/RectangularMatrix.H

@@ -80,6 +80,11 @@ public:
         //- initializing all elements to the given value
         inline RectangularMatrix(const label m, const label n, const Type& val);
 
+        //- Construct for given number of rows/columns
+        //- initializing all elements to zero, and diagonal to one
+        template<class AnyType>
+        inline RectangularMatrix(const labelPair& dims, const Identity<AnyType>);
+
         //- Construct given number of rows/columns
         inline explicit RectangularMatrix(const labelPair& dims);
 

src/OpenFOAM/matrices/RectangularMatrix/RectangularMatrixI.H

@@ -80,6 +80,23 @@ inline Foam::RectangularMatrix<Type>::RectangularMatrix
 {}
 
 
+template<class Type>
+template<class AnyType>
+inline Foam::RectangularMatrix<Type>::RectangularMatrix
+(
+    const labelPair& dims,
+    const Identity<AnyType>
+)
+:
+    Matrix<RectangularMatrix<Type>, Type>(dims.first(), dims.second(), Zero)
+{
+    for (label i = 0; i < min(dims.first(), dims.second()); ++i)
+    {
+        this->operator()(i, i) = pTraits<Type>::one;
+    }
+}
+
+
 template<class Type>
 inline Foam::RectangularMatrix<Type>::RectangularMatrix
 (