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/* Copyright (c) 1997-2024
Ewgenij Gawrilow, Michael Joswig, and the polymake team
Technische Universität Berlin, Germany
https://polymake.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, or (at your option) any
later version: http://www.gnu.org/licenses/gpl.txt.
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.
--------------------------------------------------------------------------------
*/
#pragma once
#include "polymake/GenericMatrix.h"
#include "polymake/GenericVector.h"
namespace polymake { namespace polytope {
/** @retval alpha>=0 : P=FacetPoint+alpha*ViewRay lies on the nearest neighbor facet hyperplane
alpha<0 : no intersection OR FacetPoint violates some of the neighbor facet constraints
*/
template <typename FMatrix, typename FVector, typename VVector, typename E>
E schlegel_nearest_neighbor_crossing (const GenericMatrix<FMatrix,E>& F,
const GenericVector<FVector,E>& FacetPoint,
const GenericVector<VVector,E>& ViewRay
)
{
E alpha(-1);
bool constrained=false;
for (auto nf=entire(rows(F)); !nf.at_end(); ++nf) {
const E Fr=(*nf)*ViewRay;
if (Fr<0) { // intersection on the negative side
const E alpha_here=-((*nf)*FacetPoint)/Fr;
if (!constrained || alpha_here < alpha) {
constrained=true;
alpha=alpha_here;
}
}
}
return alpha;
}
// FacetPoint=Origin implicitly
template <typename FMatrix, typename VVector, typename E>
E schlegel_nearest_neighbor_crossing (const GenericMatrix<FMatrix,E>& F,
const GenericVector<VVector,E>& ViewRay
)
{
E alpha(-1);
bool constrained=false;
for (auto nf=entire(rows(F)); !nf.at_end(); ++nf) {
const E Fr=(*nf)*ViewRay;
if (Fr<0) { // intersection on the negative side
const E alpha_here=-((*nf)[0]/Fr);
if (!constrained || alpha_here < alpha) {
constrained=true;
alpha=alpha_here;
}
}
}
return alpha;
}
} }
// Local Variables:
// mode:C++
// c-basic-offset:3
// indent-tabs-mode:nil
// End:
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