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/**
* @file
* Solve an instance of the "Variable Placement with Separation
* Constraints" problem.
*/
/*
* Authors:
* Tim Dwyer <tgdwyer@gmail.com>
*
* Copyright (C) 2005 Authors
*
* Released under GNU LGPL. Read the file 'COPYING' for more information.
*/
//
// TODO: Really, we should have three classes: VPSC, IncrementalVPSC and
// StaticVPSC, where the latter two inherit from VPSC. StaticVPSC would be
// the equivalent of what is currently VPSC.
// Also, a lot of the code specific to one or other of these concrete
// implementations should be moved from Block and Blocks: e.g. mergeLeft etc.
//
#ifndef SEEN_REMOVEOVERLAP_SOLVE_VPSC_H
#define SEEN_REMOVEOVERLAP_SOLVE_VPSC_H
#include <vector>
namespace vpsc {
class Variable;
class Constraint;
class Blocks;
/**
* Variable Placement with Separation Constraints problem instance
*/
class Solver {
public:
/**
* Produces a feasible - though not necessarily optimal - solution by
* examining blocks in the partial order defined by the directed acyclic
* graph of constraints. For each block (when processing left to right) we
* maintain the invariant that all constraints to the left of the block
* (incoming constraints) are satisfied. This is done by repeatedly merging
* blocks into bigger blocks across violated constraints (most violated
* first) fixing the position of variables inside blocks relative to one
* another so that constraints internal to the block are satisfied.
*/
virtual void satisfy();
/**
* Calculate the optimal solution. After using satisfy() to produce a
* feasible solution, refine() examines each block to see if further
* refinement is possible by splitting the block. This is done repeatedly
* until no further improvement is possible.
*/
virtual void solve();
Solver(const unsigned n, Variable* const vs[], const unsigned m, Constraint *cs[]);
virtual ~Solver();
Constraint** getConstraints(unsigned &m) { m=this->m; return cs; }
const Variable* const * getVariables(unsigned &n) { n=this->n; return vs; }
protected:
Blocks *bs;
unsigned m;
Constraint **cs;
unsigned n;
const Variable* const *vs;
void printBlocks();
private:
void refine();
bool constraintGraphIsCyclic(const unsigned n, Variable* const vs[]);
bool blockGraphIsCyclic();
};
class IncSolver : public Solver {
public:
unsigned splitCnt;
/**
* incremental version of satisfy that allows refinement after blocks are
* moved.
*
* - move blocks to new positions
* - repeatedly merge across most violated constraint until no more
* violated constraints exist
*
* Note: there is a special case to handle when the most violated constraint
* is between two variables in the same block. Then, we must split the block
* over an active constraint between the two variables. We choose the
* constraint with the most negative lagrangian multiplier.
*/
void satisfy();
void solve();
void moveBlocks();
void splitBlocks();
IncSolver(const unsigned n, Variable* const vs[], const unsigned m, Constraint *cs[]);
private:
typedef std::vector<Constraint*> ConstraintList;
ConstraintList inactive;
/**
* Scan constraint list for the most violated constraint, or the first equality
* constraint.
*/
Constraint* mostViolated(ConstraintList &l);
};
}
#endif // SEEN_REMOVEOVERLAP_SOLVE_VPSC_H
/*
Local Variables:
mode:c++
c-file-style:"stroustrup"
c-file-offsets:((innamespace . 0)(inline-open . 0)(case-label . +))
indent-tabs-mode:nil
fill-column:99
End:
*/
// vim: filetype=cpp:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:fileencoding=utf-8:textwidth=99 :
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