/*************************************************************************** * blitz/zero.h          Zero elements * * $Id: zero.h,v 1.5 2003/12/11 03:44:22 julianc Exp $ * * Copyright (C) 1997-2001 Todd Veldhuizen <tveldhui@oonumerics.org> * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public License * as published by the Free Software Foundation; either version 2 * of the License, or (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the * GNU General Public License for more details. * * Suggestions:          blitz-dev@oonumerics.org * Bugs:                 blitz-bugs@oonumerics.org * * For more information, please see the Blitz++ Home Page: *    http://oonumerics.org/blitz/ * ***************************************************************************//* * The purpose of the ZeroElement class is to provide an lvalue for * non-const element access of matrices with zero elements.  For * example, a tridiagonal matrix has many elements which are * always zero: * * [ x x 0 0 ] * [ x x x 0 ] * [ 0 x x x ] * [ 0 0 x x ] * * To implement an operator()(int i, int j) for a tridiagonal * matrix which may be used as an lvalue * * e.g. Matrix<double, Tridiagonal> M(4,4); *      M(1,2) = 3.0L; * * some way of returning an lvalue for the zero elements is needed. * (Either that, or an intermediate class must be returned -- but * this is less efficient).  The solution used for the Blitz++ * library is to have a unique zero element for each numeric * type (float, double, etc.).  This zero element is then * returned as an lvalue when needed. * * The disadvantage is the possibility of setting the global * zero-element to something non-zero.   */#ifndef BZ_ZERO_H#define BZ_ZERO_H#ifndef BZ_BLITZ_H #include <blitz/blitz.h>#endifBZ_NAMESPACE(blitz)template<typename P_numtype>class ZeroElement {public:    typedef P_numtype T_numtype;    static T_numtype& zero()    {         return zero_;     }private:    static T_numtype zero_;};// Specialization of ZeroElement for complex<float>, complex<double>,// and complex<long double>#define BZZERO_DECLARE(T)            \  template<>                         \  class ZeroElement<T > {            \  public:                            \    static T& zero()                 \    { return zero_; }                \  private:                           \    static T zero_;                  \  }#ifdef BZ_HAVE_COMPLEX  BZZERO_DECLARE(complex<float>);  BZZERO_DECLARE(complex<double>);  BZZERO_DECLARE(complex<long double>);#endif // BZ_HAVE_COMPLEX// initialization of static data member for general class templatetemplate<typename P_numtype>P_numtype ZeroElement<P_numtype>::zero_ = 0;BZ_NAMESPACE_END#endif // BZ_ZERO_H