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/**************************************************************************
* *
* Regina - A Normal Surface Theory Calculator *
* Computational Engine *
* *
* Copyright (c) 1999-2009, 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. *
* *
* 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. *
* *
**************************************************************************/
/* end stub */
#include "triangulation/ntriangulation.h"
namespace regina {
const NGroupPresentation& NTriangulation::getFundamentalGroup() const {
if (fundamentalGroup.known())
return *fundamentalGroup.value();
NGroupPresentation* ans = new NGroupPresentation();
if (getNumberOfTetrahedra() == 0)
return *(fundamentalGroup = ans);
// Find a maximal forest in the dual 1-skeleton.
// Note that this will ensure the skeleton has been calculated.
stdhash::hash_set<NFace*, HashPointer> forest;
maximalForestInDualSkeleton(forest);
// Each non-boundary not-in-forest face is a generator.
// Each non-boundary edge is a relation.
unsigned long nBdryFaces = 0;
for (BoundaryComponentIterator bit = boundaryComponents.begin();
bit != boundaryComponents.end(); bit++)
nBdryFaces += (*bit)->getNumberOfFaces();
long nGens = getNumberOfFaces() - nBdryFaces - forest.size();
// Insert the generators.
ans->addGenerator(nGens);
// Find out which face corresponds to which generator.
long *genIndex = new long[getNumberOfFaces()];
long i = 0;
for (FaceIterator fit = faces.begin(); fit != faces.end(); fit++)
if ((*fit)->isBoundary() || forest.count(*fit))
genIndex[fit - faces.begin()] = -1;
else
genIndex[fit - faces.begin()] = i++;
// Run through each edge and put the relations in the matrix.
std::deque<NEdgeEmbedding>::const_iterator embit;
NTetrahedron* currTet;
NFace* face;
int currTetFace;
long faceGenIndex;
NGroupExpression* rel;
for (EdgeIterator eit = edges.begin(); eit != edges.end(); eit++)
if (! (*eit)->isBoundary()) {
// Put in the relation corresponding to this edge.
rel = new NGroupExpression();
for (embit = (*eit)->getEmbeddings().begin();
embit != (*eit)->getEmbeddings().end(); embit++) {
currTet = (*embit).getTetrahedron();
currTetFace = (*embit).getVertices()[2];
face = currTet->getFace(currTetFace);
faceGenIndex = genIndex[faceIndex(face)];
if (faceGenIndex >= 0) {
if ((face->getEmbedding(0).getTetrahedron() == currTet) &&
(face->getEmbedding(0).getFace() == currTetFace))
rel->addTermLast(faceGenIndex, 1);
else
rel->addTermLast(faceGenIndex, -1);
}
}
ans->addRelation(rel);
}
// Tidy up.
delete[] genIndex;
ans->intelligentSimplify();
return *(fundamentalGroup = ans);
}
} // namespace regina
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