File: maxadmissible-impl.h

package info (click to toggle)
regina-normal 5.1-6
  • links: PTS
  • area: main
  • in suites: bullseye, buster, sid
  • size: 54,488 kB
  • sloc: cpp: 142,029; ansic: 19,218; xml: 9,844; objc: 7,729; perl: 1,190; python: 623; sh: 614; makefile: 34
file content (167 lines) | stat: -rw-r--r-- 6,869 bytes parent folder | download | duplicates (2)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167

/**************************************************************************
 *                                                                        *
 *  Regina - A Normal Surface Theory Calculator                           *
 *  Computational Engine                                                  *
 *                                                                        *
 *  Copyright (c) 1999-2016, Ben Burton                                   *
 *  For further details contact Ben Burton (bab@debian.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.                       *
 *                                                                        *
 *  As an exception, when this program is distributed through (i) the     *
 *  App Store by Apple Inc.; (ii) the Mac App Store by Apple Inc.; or     *
 *  (iii) Google Play by Google Inc., then that store may impose any      *
 *  digital rights management, device limits and/or redistribution        *
 *  restrictions that are required by its terms of service.               *
 *                                                                        *
 *  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.                              *
 *                                                                        *
 *  You should have received a copy of the GNU General Public             *
 *  License along with this program; if not, write to the Free            *
 *  Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston,       *
 *  MA 02110-1301, USA.                                                   *
 *                                                                        *
 **************************************************************************/

/*! \file enumerate/maxadmissible-impl.h
 *  \brief Contains implementations of template functions from maxadmissible.h.
 *
 *  This file is automatically included from maxadmissible.h; there
 *  is no need for end users to include it explicitly.
 */

#ifndef __MAXADMISSIBLE_IMPL_H
#ifndef __DOXYGEN
#define __MAXADMISSIBLE_IMPL_H
#endif

#include "enumerate/enumconstraints.h"
#include "enumerate/maxadmissible.h"
#include <algorithm>
#include <list>

namespace regina {

template <class BitmaskType, class RayIterator>
std::vector<BitmaskType>* MaxAdmissible::enumerate(
        RayIterator beginExtremalRays, RayIterator endExtremalRays,
        const EnumConstraints* constraints) {
    if (beginExtremalRays == endExtremalRays) {
        // Input is empty, so output is empty.
        return new std::vector<BitmaskType>();
    }

    size_t dim = (*beginExtremalRays).size();
    BitmaskType b(dim);
    int i;

    // Rewrite the constraints as bitmasks.
    std::vector<BitmaskType> constMasks;
    if (constraints) {
        EnumConstraints::const_iterator cit;
        std::set<unsigned long>::const_iterator sit; 
        for (cit = constraints->begin(); cit != constraints->end(); ++cit) {
            b.reset();
            for (sit = cit->begin(); sit != cit->end(); ++sit)
                b.set(*sit, true);
            constMasks.push_back(b);
        }
    }

    // Create a set of bitmasks representing the admissible 1-faces of
    // the cone, i.e., the set of admissible extremal rays.
    std::vector<BitmaskType> rays;
    for (RayIterator rit = beginExtremalRays; rit != endExtremalRays; ++rit) {
        for (i = 0; i < dim; ++i)
            b.set(i, (*rit)[i] != 0);
        rays.push_back(b);
    }

    // Create a working set of admissible faces.
    // We initialise this to the set of all admissible 1-faces, as above.
    std::list<BitmaskType> faces(rays.begin(), rays.end());

    // Create the final set of faces to return.
    std::vector<BitmaskType>* maxFaces = new std::vector<BitmaskType>();

    // Keep expanding the faces using additional extremal rays until we can
    // expand no more.
    // The ith iteration of the following loop enumerates _all_ admissible
    // faces of dimension i+1, and identifies all _maximal_ admissible
    // faces of dimension i.
    std::list<BitmaskType> nextDim;
    typename std::vector<BitmaskType>::const_iterator r, c;
    typename std::list<BitmaskType>::const_iterator f;
    typename std::list<BitmaskType>::iterator n, next;
    bool isMax, broken;
    while (! faces.empty()) {
        for (f = faces.begin(); f != faces.end(); ++f) {
            // Expand this face by combining with other extremal rays.
            isMax = true;
            for (r = rays.begin(); r != rays.end(); ++r) {
                BitmaskType comb(*f);
                comb |= *r;

                // Ignore rays already in this face.
                if (comb == *f)
                    continue;

                // Ignore rays that will break admissibility.
                broken = false;
                for (c = constMasks.begin(); c != constMasks.end(); ++c) {
                    b = comb;
                    b &= *c;
                    if (! b.atMostOneBit()) {
                        broken = true;
                        break;
                    }
                }
                if (broken)
                    continue;

                // comb expands *f to a higher-dimensional superface.
                isMax = false;

                // Strip out duplicates, and also strip out superfaces of
                // too high a dimension (since we only want to step up one
                // dimension at a time).
                broken = false;
                n = nextDim.begin();
                while (n != nextDim.end()) {
                    next = n;
                    ++next;
                    if (*n <= comb) {
                        // comb has too high a dimension, or is a duplicate.
                        broken = true;
                        break;
                    }
                    if (comb <= *n) {
                        // *n has too high a dimension.
                        nextDim.erase(n);
                    }
                    n = next;
                }
                if (! broken)
                    nextDim.push_back(comb);
            }
            if (isMax)
                maxFaces->push_back(*f);
        }
        std::swap(nextDim, faces);
        nextDim.clear();
    }

    // All done!
    return maxFaces;
}

} // namespace regina

#endif