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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 <cstdlib>
#include "triangulation/ntriangulation.h"
// Affects the number of random 4-4 moves attempted during simplification.
#define COEFF_4_4 3
namespace regina {
bool NTriangulation::intelligentSimplify() {
bool changed;
// Don't automatically fire a change event - we don't know in
// advance if changes will be made or not.
{ // Begin scope for change event block.
ChangeEventBlock block(this, false);
// Reduce to a local minimum.
changed = simplifyToLocalMinimum(true);
// Clone to work with when we might want to roll back changes.
NTriangulation* use;
// Variables used for selecting random 4-4 moves.
std::vector<std::pair<NEdge*, int> > fourFourAvailable;
std::pair<NEdge*, int> fourFourChoice;
unsigned long fourFourAttempts;
unsigned long fourFourCap;
NEdge* edge;
EdgeIterator eit;
int axis;
while (true) {
// --- Random 4-4 moves ---
// Clone the triangulation and start making changes that might or
// might not lead to a simplification.
// If we've already simplified then there's no need to use a
// separate clone since we won't need to undo further changes.
use = (changed ? this : new NTriangulation(*this));
// Make random 4-4 moves.
fourFourAttempts = fourFourCap = 0;
while (true) {
// Calculate the list of available 4-4 moves.
fourFourAvailable.clear();
// Use getEdges() to ensure the skeleton has been calculated.
for (eit = use->getEdges().begin();
eit != use->getEdges().end(); eit++) {
edge = *eit;
for (axis = 0; axis < 2; axis++)
if (use->fourFourMove(edge, axis, true, false))
fourFourAvailable.push_back(
std::make_pair(edge, axis));
}
// Increment fourFourCap if needed.
if (fourFourCap < COEFF_4_4 * fourFourAvailable.size())
fourFourCap = COEFF_4_4 * fourFourAvailable.size();
// Have we tried enough 4-4 moves?
if (fourFourAttempts >= fourFourCap)
break;
// Perform a random 4-4 move on the clone.
fourFourChoice = fourFourAvailable[
static_cast<unsigned>(rand()) % fourFourAvailable.size()];
use->fourFourMove(fourFourChoice.first, fourFourChoice.second,
false, true);
// See if we can simplify now.
if (use->simplifyToLocalMinimum(true)) {
// We have successfully simplified!
// Start all over again.
fourFourAttempts = fourFourCap = 0;
} else
fourFourAttempts++;
}
// Sync the real triangulation with the clone if appropriate.
if (use != this) {
// At this point, changed == false.
if (use->getNumberOfTetrahedra() < getNumberOfTetrahedra()) {
// The 4-4 moves were successful; accept them.
cloneFrom(*use);
changed = true;
}
delete use;
}
// At this point we have decided that 4-4 moves will help us
// no more.
// --- Open book and close book moves ---
if (hasBoundaryFaces()) {
// Clone again, always -- we don't want to create gratuitous
// boundary faces if they won't be of any help.
use = new NTriangulation(*this);
// Perform every book opening move we can find.
FaceIterator fit;
bool opened = false;
bool openedNow = true;
while (openedNow) {
openedNow = false;
for (fit = use->getFaces().begin();
fit != use->getFaces().end(); ++fit)
if (use->openBook(*fit, true, true)) {
opened = openedNow = true;
break;
}
}
// If we're lucky, we now have an edge that we can collapse.
if (opened) {
if (use->simplifyToLocalMinimum(true)) {
// Yay!
cloneFrom(*use);
changed = true;
} else {
// No good.
// Ditch use and don't open anything.
opened = false;
}
}
delete use;
// If we did any book opening stuff, start all over again.
if (opened)
continue;
// If we've made it this far then there seems to be
// nothing left to do.
//
// Perform book *closing* moves to simplify the boundary
// of the triangulation, even if this does not actually
// reduce the number of tetrahedra.
//
// Since we always want to simplify the boundary, make
// the changes directly to this triangulation.
bool closed = false;
EdgeIterator eit;
for (eit = getEdges().begin(); eit != getEdges().end(); ++eit)
if (closeBook(*eit, true, true)) {
closed = true;
changed = true;
// We don't actually care whether we reduce the
// number of tetrahedra or not. Ignore the
// return value from simplifyToLocalMinimum().
simplifyToLocalMinimum(true);
break;
}
// If we *did* manage to close a book, there might be
// further internal simplifications that we can now do.
// Back to the top.
if (closed)
continue;
}
// Nothing more we can do here.
break;
}
} // End scope for change event block.
if (changed)
fireChangedEvent();
return changed;
}
bool NTriangulation::simplifyToLocalMinimum(bool perform) {
EdgeIterator eit;
VertexIterator vit;
BoundaryComponentIterator bit;
NEdge* edge;
NBoundaryComponent* bc;
unsigned long nFaces;
unsigned long iFace;
// unsigned long nEdges;
// unsigned long iEdge;
// std::deque<NEdgeEmbedding>::const_iterator embit, embbeginit, embendit;
bool changed = false; // Has anything changed ever (for return value)?
bool changedNow = true; // Did we just change something (for loop control)?
// Don't automatically fire a change event - we don't know in
// advance if changes will be made or not.
{ // Begin scope for change event block.
ChangeEventBlock block(this, false);
while (changedNow) {
changedNow = false;
if (! calculatedSkeleton) {
calculateSkeleton();
}
// Crush edges if we can.
if (vertices.size() > components.size() &&
vertices.size() > boundaryComponents.size()) {
for (eit = edges.begin(); eit != edges.end(); ++eit) {
edge = *eit;
if (collapseEdge(edge, true, perform)) {
changedNow = changed = true;
break;
}
}
if (changedNow) {
if (perform)
continue;
else
return true;
}
}
// Look for internal simplifications.
for (eit = edges.begin(); eit != edges.end(); eit++) {
edge = *eit;
if (threeTwoMove(edge, true, perform)) {
changedNow = changed = true;
break;
}
if (twoZeroMove(edge, true, perform)) {
changedNow = changed = true;
break;
}
if (twoOneMove(edge, 0, true, perform)) {
changedNow = changed = true;
break;
}
if (twoOneMove(edge, 1, true, perform)) {
changedNow = changed = true;
break;
}
}
if (changedNow) {
if (perform)
continue;
else
return true;
}
for (vit = vertices.begin(); vit != vertices.end(); vit++) {
if (twoZeroMove(*vit, true, perform)) {
changedNow = changed = true;
break;
}
}
if (changedNow) {
if (perform)
continue;
else
return true;
}
// Look for boundary simplifications.
if (hasBoundaryFaces()) {
for (bit = boundaryComponents.begin();
bit != boundaryComponents.end(); bit++) {
bc = *bit;
// Run through faces of this boundary component looking
// for shell boundary moves.
nFaces = (*bit)->getNumberOfFaces();
for (iFace = 0; iFace < nFaces; iFace++) {
if (shellBoundary((*bit)->getFace(iFace)->
getEmbedding(0).getTetrahedron(),
true, perform)) {
changedNow = changed = true;
break;
}
}
if (changedNow)
break;
}
if (changedNow) {
if (perform)
continue;
else
return true;
}
}
}
} // End scope for change event block.
if (changed)
fireChangedEvent();
return changed;
}
} // namespace regina
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