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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 "triangulation/dim3.h"
#include "triangulation/dim4.h"
#include <sstream>
namespace regina {
Face<4, 0>::~Face() {
// Deleting null is always safe.
delete link_;
}
const Triangulation<3>& Face<4, 0>::buildLink() const {
if (! link_) {
// Note: we need to insert tetrahedra in the correct order, as
// specified in the buildLink() documentation.
// Build a map from (pentachoron, vertex) pairs to indices into
// embeddings().
FixedArray<size_t> map(5 * triangulation().size());
{
size_t i = 0;
for (const auto& emb : embeddings())
map[5 * emb.simplex()->index() + emb.face()] = i++;
}
// Now build the triangulation.
auto* ans = new Triangulation<3>();
ans->newTetrahedra(degree());
for (const auto& emb : embeddings()) {
// Glue this piece of vertex link to any adjacent pieces of
// vertex link.
size_t pentIdx = emb.simplex()->index();
for (int f = 0; f < 5; ++f) {
if (f == emb.face())
continue;
auto adjPent = emb.simplex()->adjacentPentachoron(f);
if (! adjPent)
continue;
// Make sure we perform each gluing in one direction only.
size_t adjPentIdx = adjPent->index();
if (adjPentIdx > pentIdx)
continue;
int adjFacet = emb.simplex()->adjacentFacet(f);
if (adjPentIdx == pentIdx && adjFacet > f)
continue;
// This tetrahedron is adjacent to a previously-seen
// tetrahedron. Make the gluing.
int adjVertexIdx = emb.simplex()->adjacentGluing(f)[emb.face()];
Perm<5> tetVertices =
emb.simplex()->tetrahedronMapping(emb.face());
Perm<5> adjTetVertices =
adjPent->tetrahedronMapping(adjVertexIdx);
ans->tetrahedron(map[5 * pentIdx + emb.face()])->join(
tetVertices.pre(f),
ans->tetrahedron(map[5 * adjPentIdx + adjVertexIdx]),
Perm<4>::contract(
adjTetVertices.inverse() *
emb.simplex()->adjacentGluing(f) *
tetVertices));
}
}
// This is a construct-on-demand member; cast away constness to
// set it here.
const_cast<Vertex<4>*>(this)->link_ = ans;
}
return *link_;
}
Isomorphism<4> Face<4, 0>::buildLinkInclusion() const {
Isomorphism<4> inclusion(degree());
size_t i = 0;
for (auto it = begin(); it != end(); ++it, ++i) {
inclusion.pentImage(i) = it->pentachoron()->index();
inclusion.facetPerm(i) = it->pentachoron()->tetrahedronMapping(
it->vertex());
}
return inclusion;
}
} // namespace regina
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