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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 <cassert>
#include <iomanip>
#include <iostream>
#include <sstream>
#include "algebra/intersectionform.h"
#include "triangulation/dim3.h"
#include "triangulation/dim4.h"
#include "utilities/xmlutils.h"
namespace regina {
Triangulation<4>::Triangulation(const std::string& description) {
try {
*this = fromIsoSig(description);
return;
} catch (const InvalidArgument&) {
}
throw InvalidArgument("The given string could not be interpreted "
"as representing a 4-dimensional triangulation");
}
long Triangulation<4>::eulerCharManifold() const {
if (! isValid())
throw FailedPrecondition("eulerCharManifold() requires a valid "
"triangulation");
// Begin with V - E + F - T + P.
// This call to eulerCharTri() also ensures that the skeleton has
// been calculated.
long ans = eulerCharTri();
// Truncate any ideal vertices.
if (vertexLinkSummary_ != 0) {
// There *might* be ideal vertices.
// (Actually, since this routine has validity as a precondition,
// and since the skeleton has been computed by this point, we should
// have vertexLinkSummary_ non-negative at this point, which means
// there *are* ideal vertices. But this guarantee is stronger than
// we actually need here.)
for (auto bc : boundaryComponents())
if (bc->isIdeal()) {
// This boundary component consists of a single _valid_ ideal
// vertex, which must therefore have a link that is a valid
// closed 3-manifold triangulation. It follows that the Euler
// characteristic of the vertex link is zero, and so truncating
// the vertex has exactly the following effect:
--ans;
}
}
return ans;
}
Triangulation<4>::Triangulation(const Triangulation& src, bool cloneProps,
bool cloneLocks) : TriangulationBase<4>(src, cloneProps, cloneLocks),
vertexLinkSummary_(src.vertexLinkSummary_) /* always cloned */ {
// For other properties, the user gets to decide:
if (! cloneProps)
return;
prop_ = src.prop_;
// We do not need to copy any properties that are computed on demand with
// the rest of the skeleton; however, at the time of writing there
// are no such properties in the Triangulation<4> class anyway.
}
void Triangulation<4>::clearAllProperties() {
clearBaseProperties();
if (! topologyLocked()) {
vertexLinkSummary_ = -1; /* not yet computed */
prop_.H2_.reset();
}
}
void Triangulation<4>::swap(Triangulation<4>& other) {
if (&other == this)
return;
// We use a basic PacketChangeSpan here, not a richer ChangeAndClearSpan,
// since we do not want to touch computed properties. Our intention here
// is to swap them, not clear them.
PacketChangeSpan span1(*this);
PacketChangeSpan span2(other);
// Note: swapBaseData() calls Snapshottable::swap().
swapBaseData(other);
// Properties stored directly:
std::swap(vertexLinkSummary_, other.vertexLinkSummary_);
// Properties stored using std::... helper classes:
prop_.H2_.swap(other.prop_.H2_);
}
IntersectionForm Triangulation<4>::intersectionForm() const {
if (isEmpty())
throw FailedPrecondition("Computing intersection form "
"requires a non-empty triangulation.");
if (! isValid())
throw FailedPrecondition("Computing intersection form "
"requires a valid triangulation.");
if (! isOrientable())
throw FailedPrecondition("Computing intersection form "
"requires an orientable triangulation.");
if (! isClosed())
throw FailedPrecondition("Computing intersection form "
"requires a closed triangulation.");
MarkedAbelianGroup h2(dualBoundaryMap<2>(), dualBoundaryMap<3>());
MatrixInt map = dualToPrimal<2>();
size_t rank = h2.rank();
size_t dim = countTriangles();
std::vector<VectorInt> dualBasis, primalBasis;
dualBasis.reserve(dim);
primalBasis.reserve(dim);
for (size_t i = 0; i < rank; ++i) {
dualBasis.emplace_back(h2.freeRep(i));
primalBasis.emplace_back(map * dualBasis.back());
}
std::vector<bool> sign(dim);
for (size_t i = 0; i < dim; ++i) {
const auto emb = triangle(i)->front();
sign[i] = (emb.simplex()->orientation() == emb.vertices().sign());
}
MatrixInt form(rank, rank);
for (size_t i = 0; i < rank; ++i)
for (size_t j = i; j < rank; ++j) {
for (size_t k = 0; k < dim; ++k) {
Integer count = dualBasis[i][k] * primalBasis[j][k];
if (count != 0) {
if (sign[k])
form.entry(i, j) += count;
else
form.entry(i, j) -= count;
}
}
if (j != i)
form.entry(j, i) = form.entry(i, j);
}
return IntersectionForm(std::move(form));
}
} // namespace regina
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