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Regina 7.3 Calculation Engine
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Implements a modified double description method for polytope vertex enumeration. More...
#include <enumerate/doubledescription.h>
Static Public Member Functions | |
| template<class RayClass , typename Action > | |
| static void | enumerate (Action &&action, const MatrixInt &subspace, const ValidityConstraints &constraints, ProgressTracker *tracker=nullptr, size_t initialRows=0) |
| Determines the extremal rays of the intersection of the n-dimensional non-negative orthant with the given linear subspace. More... | |
Implements a modified double description method for polytope vertex enumeration.
For details of the underlying algorithm, see "Optimizing the double description method for normal surface enumeration", Benjamin A. Burton, Math. Comp. 79 (2010), 453-484.
All routines of interest within this class are static; no object of this class should ever be created.
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Determines the extremal rays of the intersection of the n-dimensional non-negative orthant with the given linear subspace.
The resulting rays will be of the class RayClass, and will be passed into the given action function one at a time.
The non-negative orthant is an n-dimensional cone with its vertex at the origin. The extremal rays of this cone are the n non-negative coordinate axes. This cone also has n facets, where the ith facet is the non-negative orthant of the plane perpendicular to the ith coordinate axis.
This routine takes a linear subspace, defined by the intersection of a set of hyperplanes through the origin (this subspace is described as a matrix, with each row giving the equation for one hyperplane).
The purpose of this routine is to compute the extremal rays of the new cone formed by intersecting the original cone with this linear subspace. The resulting list of extremal rays will contain no duplicates or redundancies.
Parameter constraints may contain a set of validity constraints, in which case this routine will only return valid extremal rays. Each validity constraint is of the form "an extremal ray may only lie outside at most one of these facets of the original cone"; see the ValidityConstraints class for details. These contraints have the important property that, although validity is not preserved under convex combination, invalidity is.
An optional progress tracker may be passed. If so, this routine will update the percentage progress and poll for cancellation requests. It will be assumed that an appropriate stage has already been declared via ProgressTracker::newStage() before this routine is called, and that ProgressTracker::setFinished() will be called after this routine returns.
For each of the resulting extremal rays, this routine will call action (which must be a function or some other callable object). This action should return void, and must take exactly one argument, which will be the extremal ray stored using RayClass. The argument will be passed as an rvalue; a typical action would take it as an rvalue reference (RayClass&&) and move its contents into some other more permanent storage.
enumerate(subspace, constraints, tracker, initialRows), and it returns a Python list containing all extremal rays. In both versions, the argument RayClass is fixed as VectorInt. The global interpreter lock will be released while this function runs, so you can use it with Python-based multithreading.| action | a function (or other callable object) that will be called for each extremal ray. This function must take a single argument, which will be passed as an rvalue of type RayClass. |
| subspace | a matrix defining the linear subspace to intersect with the given cone. Each row of this matrix is the equation for one of the hyperplanes whose intersection forms this linear subspace. The number of columns in this matrix must be the dimension of the overall space in which we are working. |
| constraints | a set of validity constraints as described above, or ValidityConstraints::none if none should be imposed. |
| tracker | a progress tracker through which progress will be reported, or null if no progress reporting is required. |
| initialRows | specifies how many initial rows of subspace are to be processed in the precise order in which they appear. The remaining rows will be sorted using the PosOrder class before they are processed. |