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/**************************************************************************
* *
* Regina - A Normal Surface Theory Calculator *
* Computational Engine *
* *
* Copyright (c) 1999-2008, 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 {
void NTriangulation::maximalForestInBoundary(
stdhash::hash_set<NEdge*, HashPointer>& edgeSet,
stdhash::hash_set<NVertex*, HashPointer>& vertexSet) const {
if (! calculatedSkeleton)
calculateSkeleton();
vertexSet.clear();
edgeSet.clear();
for (BoundaryComponentIterator bit = boundaryComponents.begin();
bit != boundaryComponents.end(); bit++)
stretchBoundaryForestFromVertex((*bit)->getVertex(0),
edgeSet, vertexSet);
}
void NTriangulation::stretchBoundaryForestFromVertex(NVertex* from,
stdhash::hash_set<NEdge*, HashPointer>& edgeSet,
stdhash::hash_set<NVertex*, HashPointer>& vertexSet) const {
vertexSet.insert(from);
std::vector<NVertexEmbedding>::const_iterator it =
from->getEmbeddings().begin();
NTetrahedron* tet;
NVertex* otherVertex;
NEdge* edge;
int vertex, yourVertex;
while (it != from->getEmbeddings().end()) {
const NVertexEmbedding& emb = *it;
tet = emb.getTetrahedron();
vertex = emb.getVertex();
for (yourVertex = 0; yourVertex < 4; yourVertex++) {
if (vertex == yourVertex)
continue;
edge = tet->getEdge(edgeNumber[vertex][yourVertex]);
if (! (edge->isBoundary()))
continue;
otherVertex = tet->getVertex(yourVertex);
if (! vertexSet.count(otherVertex)) {
edgeSet.insert(edge);
stretchBoundaryForestFromVertex(otherVertex, edgeSet,
vertexSet);
}
}
it++;
}
}
void NTriangulation::maximalForestInSkeleton(
stdhash::hash_set<NEdge*, HashPointer>& edgeSet,
bool canJoinBoundaries) const {
if (! calculatedSkeleton)
calculateSkeleton();
stdhash::hash_set<NVertex*, HashPointer> vertexSet;
stdhash::hash_set<NVertex*, HashPointer> thisBranch;
if (canJoinBoundaries)
edgeSet.clear();
else
maximalForestInBoundary(edgeSet, vertexSet);
for (VertexIterator vit = vertices.begin(); vit != vertices.end(); vit++)
if (! (vertexSet.count(*vit))) {
stretchForestFromVertex(*vit, edgeSet, vertexSet, thisBranch);
thisBranch.clear();
}
}
bool NTriangulation::stretchForestFromVertex(NVertex* from,
stdhash::hash_set<NEdge*, HashPointer>& edgeSet,
stdhash::hash_set<NVertex*, HashPointer>& vertexSet,
stdhash::hash_set<NVertex*, HashPointer>& thisStretch) const {
// Moves out from the vertex until we hit a vertex that has already
// been visited; then stops.
// Returns true if we make such a link.
// PRE: Such a link has not already been made.
vertexSet.insert(from);
thisStretch.insert(from);
std::vector<NVertexEmbedding>::const_iterator it =
from->getEmbeddings().begin();
NTetrahedron* tet;
NVertex* otherVertex;
int vertex, yourVertex;
bool madeLink = false;
while (it != from->getEmbeddings().end()) {
const NVertexEmbedding& emb = *it;
tet = emb.getTetrahedron();
vertex = emb.getVertex();
for (yourVertex = 0; yourVertex < 4; yourVertex++) {
if (vertex == yourVertex)
continue;
otherVertex = tet->getVertex(yourVertex);
if (thisStretch.count(otherVertex))
continue;
madeLink = vertexSet.count(otherVertex);
edgeSet.insert(tet->getEdge(edgeNumber[vertex][yourVertex]));
if (! madeLink)
madeLink =
stretchForestFromVertex(otherVertex, edgeSet, vertexSet,
thisStretch);
if (madeLink)
return true;
}
it++;
}
return false;
}
bool NTriangulation::crushMaximalForest() {
// First obtain a maximal forest in the 1-skeleton.
stdhash::hash_set<NEdge*, HashPointer> cEdges;
maximalForestInSkeleton(cEdges, false);
/* --- DEBUGGING OUTPUT ---
{
stdhash::hash_set<NFace*, HashPointer> dual;
maximalForestInDualSkeleton(dual);
cerr << "Dual Faces: " << dual.size() << '\n';
NPointerSetIterator<NFace> it(dual);
while (! it.done()) {
cerr << faceIndex(*it) << ' ';
it++;
}
cerr << '\n';
}
cerr << "Edges going: " << cEdges.size() << '\n';
{
NPointerSetIterator<NEdge> it(cEdges);
while (! it.done()) {
cerr << edgeIndex(*it) << ' ';
it++;
}
cerr << '\n';
}
------------------------*/
stdhash::hash_set<NTetrahedron*, HashPointer> cTetrahedra;
// Extend this list of collapsings to faces.
NTetrahedron* tet;
TetrahedronIterator tit;
int face, edge;
int nLost;
bool changed = true;
while (changed) {
changed = false;
for (tit = tetrahedra.begin(); tit != tetrahedra.end(); tit++) {
tet = *tit;
for (face = 0; face < 4; face++) {
nLost = 0;
for (edge = 0; edge < 6; edge++) {
if (edgeStart[edge] == face || edgeEnd[edge] == face)
continue;
if (cEdges.count(tet->getEdge(edge)))
nLost++;
}
// Changed > 1 below to == 2 since we're not storing
// faces.
if (nLost == 2) {
for (edge = 0; edge < 6; edge++) {
if (edgeStart[edge] == face || edgeEnd[edge] == face)
continue;
cEdges.insert(tet->getEdge(edge));
}
changed = true;
}
}
}
}
// Finally extend this list to tetrahedra.
for (tit = tetrahedra.begin(); tit != tetrahedra.end(); tit++) {
tet = *tit;
for (edge = 0; edge < 6; edge++)
if (cEdges.count(tet->getEdge(edge))) {
cTetrahedra.insert(tet);
break;
}
}
// Are we going to change anything?
if (cTetrahedra.empty())
return false;
ChangeEventBlock block(this);
// Prepare to measure the change in topology.
/*
const NAbelianGroup& h1(getHomologyH1());
unsigned long oldComponents = components.size();
unsigned long oldRank = h1.getRank();
unsigned long oldRank2 = h1.getTorsionRank(2);
unsigned long oldRank3 = h1.getTorsionRank(3);
*/
// Reglue the surviving tetrahedra.
NTetrahedron* adjTet;
NTetrahedron* tmpTet;
NPerm adjPerm;
int adjFace, edgeFrom;
for (tit = tetrahedra.begin(); tit != tetrahedra.end(); tit++) {
tet = *tit;
if (! cTetrahedra.count(tet))
for (face = 0; face < 4; face++) {
adjTet = tet->getAdjacentTetrahedron(face);
if (adjTet == 0)
continue;
if (! cTetrahedra.count(adjTet))
continue;
adjPerm = tet->getAdjacentTetrahedronGluing(face);
adjFace = adjPerm[face];
while(1) {
// Follow through to the next face.
for (edgeFrom = 0; edgeFrom < 4; edgeFrom++) {
if (edgeFrom == adjFace)
continue;
if (! (cEdges.count(adjTet->
getEdge(edgeNumber[adjFace][edgeFrom]))))
continue;
break;
}
// Follow edge from edgeFrom to adjFace.
// The face of adjTet we now move to is edgeFrom.
tmpTet = adjTet->getAdjacentTetrahedron(edgeFrom);
if (tmpTet == 0) {
// Make the original face a boundary face.
tet->unjoin(face);
break;
}
adjPerm = adjTet->getAdjacentTetrahedronGluing(edgeFrom) *
NPerm(adjFace, edgeFrom) * adjPerm;
adjFace = adjPerm[face];
adjTet = tmpTet;
if (! (cTetrahedra.count(adjTet))) {
// Glue the original face to this safe
// tetrahedron.
tet->unjoin(face);
adjTet->unjoin(adjFace);
tet->joinTo(face, adjTet, adjPerm);
break;
}
}
}
}
// Remove the squished tetrahedra.
// For each tetrahedron, remove it and delete it.
for (stdhash::hash_set<NTetrahedron*, HashPointer>::iterator tetIt =
cTetrahedra.begin(); tetIt != cTetrahedra.end(); tetIt++) {
tetrahedra.erase(tetrahedra.begin() + tetrahedronIndex(*tetIt));
delete *tetIt;
}
// Tidy up.
gluingsHaveChanged();
// Measure the change in topology.
/*
const NAbelianGroup& newH1 = getHomologyH1();
extraTopology = extraTopology + NExtraTopology(
components.size() - oldComponents,
oldRank - newH1.getRank(),
oldRank3 - newH1.getTorsionRank(3),
oldRank2 - newH1.getTorsionRank(2)
);
*/
return true;
}
void NTriangulation::maximalForestInDualSkeleton(
stdhash::hash_set<NFace*, HashPointer>& faceSet) const {
if (! calculatedSkeleton)
calculateSkeleton();
faceSet.clear();
stdhash::hash_set<NTetrahedron*, HashPointer> visited;
for (TetrahedronIterator it = tetrahedra.begin(); it != tetrahedra.end();
it++)
if (! (visited.count(*it)))
stretchDualForestFromTet(*it, faceSet, visited);
}
void NTriangulation::stretchDualForestFromTet(NTetrahedron* tet,
stdhash::hash_set<NFace*, HashPointer>& faceSet,
stdhash::hash_set<NTetrahedron*, HashPointer>& visited) const {
visited.insert(tet);
NTetrahedron* adjTet;
for (int face = 0; face < 4; face++) {
adjTet = tet->getAdjacentTetrahedron(face);
if (adjTet)
if (! (visited.count(adjTet))) {
faceSet.insert(tet->getFace(face));
stretchDualForestFromTet(adjTet, faceSet, visited);
}
}
}
} // namespace regina
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