////   This file contains the C++ code from Program 4.23 of//   "Data Structures and Algorithms//    with Object-Oriented Design Patterns in C++"//   by Bruno R. Preiss.////   Copyright (c) 1998 by Bruno R. Preiss, P.Eng.  All rights reserved.////   http://www.pads.uwaterloo.ca/Bruno.Preiss/books/opus4/programs/pgm04_23.cpp//template <class T>Matrix<T> Matrix<T>::operator * (Matrix<T> const& arg) const{    if (numberOfColumns != arg.numberOfRows)	throw invalid_argument ("incompatible matrices");    Matrix<T> result (numberOfRows, arg.numberOfColumns);    for (unsigned int i = 0; i < numberOfRows; ++i)    {	for (unsigned int j = 0; j < arg.numberOfColumns; ++j)	{	    T sum = 0;	    for (unsigned int k = 0; k < numberOfColumns; ++k)		sum += (*this) [i][k] * arg [k][j];	    result [i][j] = sum;	}    }    return result;}