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/**************************************************************************
* *
* Regina - A Normal Surface Theory Calculator *
* Computational Engine *
* *
* Copyright (c) 1999-2025, 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, see <https://www.gnu.org/licenses/>. *
* *
**************************************************************************/
#include "algebra/abeliangroup.h"
#include "manifold/handlebody.h"
#include "triangulation/dim3.h"
#include "subcomplex/layeredchain.h"
namespace regina {
bool LayeredChain::extendAbove() {
Tetrahedron<3>* adj = top_->adjacentTetrahedron(topVertexRoles_[0]);
if (adj == bottom_ || adj == top_ || ! adj)
return false;
if (adj != top_->adjacentTetrahedron(topVertexRoles_[3]))
return false;
// Check the gluings.
Perm<4> adjRoles = top_->adjacentGluing(topVertexRoles_[0]) *
topVertexRoles_ * Perm<4>(0, 1);
if (adjRoles != top_->adjacentGluing(topVertexRoles_[3]) *
topVertexRoles_ * Perm<4>(2, 3))
return false;
// We can extend the layered chain.
top_ = adj;
topVertexRoles_ = adjRoles;
++index_;
return true;
}
bool LayeredChain::extendBelow() {
Tetrahedron<3>* adj = bottom_->adjacentTetrahedron(bottomVertexRoles_[1]);
if (adj == bottom_ || adj == top_ || ! adj)
return false;
if (adj != bottom_->adjacentTetrahedron(bottomVertexRoles_[2]))
return false;
// Check the gluings.
Perm<4> adjRoles = bottom_->adjacentGluing(bottomVertexRoles_[1])
* bottomVertexRoles_ * Perm<4>(0, 1);
if (adjRoles != bottom_->adjacentGluing(bottomVertexRoles_[2])
* bottomVertexRoles_ * Perm<4>(2, 3))
return false;
// We can extend the layered chain.
bottom_ = adj;
bottomVertexRoles_ = adjRoles;
++index_;
return true;
}
bool LayeredChain::extendMaximal() {
bool changed = false;
while (extendAbove())
changed = true;
while (extendBelow())
changed = true;
return changed;
}
void LayeredChain::reverse() {
std::swap(bottom_, top_);
Perm<4> pTmp = topVertexRoles_ * Perm<4>(1, 0, 3, 2);
topVertexRoles_ = bottomVertexRoles_ * Perm<4>(1, 0, 3, 2);
bottomVertexRoles_ = pTmp;
}
void LayeredChain::invert() {
topVertexRoles_ = topVertexRoles_ * Perm<4>(3, 2, 1, 0);
bottomVertexRoles_ = bottomVertexRoles_ * Perm<4>(3, 2, 1, 0);
}
std::unique_ptr<Manifold> LayeredChain::manifold() const {
return std::make_unique<Handlebody>(index_ <= 1 ? 0 : 1);
}
AbelianGroup LayeredChain::homology() const {
if (index_ > 1)
return AbelianGroup(1);
else
return AbelianGroup();
}
void LayeredChain::writeTextShort(std::ostream& out) const {
if (index_ == 1) {
out << "Chain(1), tetrahedron "
<< bottom_->index() << " (" << bottomVertexRoles_ << ")";
} else {
out << "Chain(" << index_ << "), tetrahedra "
<< bottom_->index() << " (" << bottomVertexRoles_ << ") .. "
<< top_->index() << " (" << topVertexRoles_ << ')';
}
}
} // namespace regina
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