Detect and process implied free variables. More...

#include <CoinPresolveImpliedFree.hpp>

Inheritance diagram for implied_free_action:

Collaboration diagram for implied_free_action:

Classes
struct	action

Public Member Functions
const char *	name () const
	A name for debug printing. More...

void	postsolve (CoinPostsolveMatrix *prob) const
	Apply the postsolve transformation for this particular presolve action. More...

virtual	~implied_free_action ()

Public Member Functions inherited from CoinPresolveAction
	CoinPresolveAction (const CoinPresolveAction *next)
	Construct a postsolve object and add it to the transformation list. More...

void	setNext (const CoinPresolveAction *nextAction)
	modify next (when building rather than passing) More...

virtual	~CoinPresolveAction ()
	Virtual destructor. More...

Static Public Member Functions
static const CoinPresolveAction *	presolve (CoinPresolveMatrix prob, const CoinPresolveAction next, int &fillLevel)

Static Public Member Functions inherited from CoinPresolveAction
static void	throwCoinError (const char error, const char ps_routine)
	Stub routine to throw exceptions. More...

Private Member Functions
	implied_free_action (int nactions, const action actions, const CoinPresolveAction next)

Private Attributes
const int	nactions_

const action *const	actions_

Additional Inherited Members
Public Attributes inherited from CoinPresolveAction
const CoinPresolveAction *	next
	The next presolve transformation. More...

Detailed Description

Detect and process implied free variables.

Consider a singleton variable x (i.e., a variable involved in only one constraint). Suppose that the bounds on that constraint, combined with the bounds on the other variables involved in the constraint, are such that even the worst case values of the other variables still imply bounds for x which are tighter than the variable's original bounds. Since x can never reach its upper or lower bounds, it is an implied free variable. Both x and the constraint can be deleted from the problem.

A similar transform for the case where the variable is not a natural column singleton is handled by subst_constraint_action.

Definition at line 29 of file CoinPresolveImpliedFree.hpp.