1 | /*************************************************************************** |
---|
2 | * blitz/zero.h Zero elements |
---|
3 | * |
---|
4 | * $Id: zero.h,v 1.5 2003/12/11 03:44:22 julianc Exp $ |
---|
5 | * |
---|
6 | * Copyright (C) 1997-2001 Todd Veldhuizen <tveldhui@oonumerics.org> |
---|
7 | * |
---|
8 | * This program is free software; you can redistribute it and/or |
---|
9 | * modify it under the terms of the GNU General Public License |
---|
10 | * as published by the Free Software Foundation; either version 2 |
---|
11 | * of the License, or (at your option) any later version. |
---|
12 | * |
---|
13 | * This program is distributed in the hope that it will be useful, |
---|
14 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
---|
15 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
---|
16 | * GNU General Public License for more details. |
---|
17 | * |
---|
18 | * Suggestions: blitz-dev@oonumerics.org |
---|
19 | * Bugs: blitz-bugs@oonumerics.org |
---|
20 | * |
---|
21 | * For more information, please see the Blitz++ Home Page: |
---|
22 | * http://oonumerics.org/blitz/ |
---|
23 | * |
---|
24 | ***************************************************************************/ |
---|
25 | |
---|
26 | /* |
---|
27 | * The purpose of the ZeroElement class is to provide an lvalue for |
---|
28 | * non-const element access of matrices with zero elements. For |
---|
29 | * example, a tridiagonal matrix has many elements which are |
---|
30 | * always zero: |
---|
31 | * |
---|
32 | * [ x x 0 0 ] |
---|
33 | * [ x x x 0 ] |
---|
34 | * [ 0 x x x ] |
---|
35 | * [ 0 0 x x ] |
---|
36 | * |
---|
37 | * To implement an operator()(int i, int j) for a tridiagonal |
---|
38 | * matrix which may be used as an lvalue |
---|
39 | * |
---|
40 | * e.g. Matrix<double, Tridiagonal> M(4,4); |
---|
41 | * M(1,2) = 3.0L; |
---|
42 | * |
---|
43 | * some way of returning an lvalue for the zero elements is needed. |
---|
44 | * (Either that, or an intermediate class must be returned -- but |
---|
45 | * this is less efficient). The solution used for the Blitz++ |
---|
46 | * library is to have a unique zero element for each numeric |
---|
47 | * type (float, double, etc.). This zero element is then |
---|
48 | * returned as an lvalue when needed. |
---|
49 | * |
---|
50 | * The disadvantage is the possibility of setting the global |
---|
51 | * zero-element to something non-zero. |
---|
52 | */ |
---|
53 | |
---|
54 | #ifndef BZ_ZERO_H |
---|
55 | #define BZ_ZERO_H |
---|
56 | |
---|
57 | #ifndef BZ_BLITZ_H |
---|
58 | #include <blitz/blitz.h> |
---|
59 | #endif |
---|
60 | |
---|
61 | BZ_NAMESPACE(blitz) |
---|
62 | |
---|
63 | template<typename P_numtype> |
---|
64 | class ZeroElement { |
---|
65 | public: |
---|
66 | typedef P_numtype T_numtype; |
---|
67 | |
---|
68 | static T_numtype& zero() |
---|
69 | { |
---|
70 | return zero_; |
---|
71 | } |
---|
72 | |
---|
73 | private: |
---|
74 | static T_numtype zero_; |
---|
75 | }; |
---|
76 | |
---|
77 | // Specialization of ZeroElement for complex<float>, complex<double>, |
---|
78 | // and complex<long double> |
---|
79 | |
---|
80 | #define BZZERO_DECLARE(T) \ |
---|
81 | template<> \ |
---|
82 | class ZeroElement<T > { \ |
---|
83 | public: \ |
---|
84 | static T& zero() \ |
---|
85 | { return zero_; } \ |
---|
86 | private: \ |
---|
87 | static T zero_; \ |
---|
88 | } |
---|
89 | |
---|
90 | #ifdef BZ_HAVE_COMPLEX |
---|
91 | BZZERO_DECLARE(complex<float>); |
---|
92 | BZZERO_DECLARE(complex<double>); |
---|
93 | BZZERO_DECLARE(complex<long double>); |
---|
94 | #endif // BZ_HAVE_COMPLEX |
---|
95 | |
---|
96 | // initialization of static data member for general class template |
---|
97 | |
---|
98 | template<typename P_numtype> |
---|
99 | P_numtype ZeroElement<P_numtype>::zero_ = 0; |
---|
100 | |
---|
101 | BZ_NAMESPACE_END |
---|
102 | |
---|
103 | #endif // BZ_ZERO_H |
---|
104 | |
---|