lp_get(+Handle, ++ParamName, -Value)

Handle

Handle to an existing solver state

ParamName

Name of parameter (atom or structure)

Value

Returned value for ParamName

Description

Retrieve information about solver state and results for the solver state represented by Handle. ParamName is the same as that for eplex_get/2, which retrieves the same information via the EplexInstance. It can be one of:

vars

Returns a term ''(X1,...,Xn) whose arity is the number of variables involved in the solver's constraint set, and whose arguments are these variables.

ints

Returns a list [Xi1,...,Xik] which is the subset of the problem variables that the solver considers to be integers.

constraints_norm

Returns a list of the problem constraints in normalised form. They may be simplified with respect to the original set that was passed to lp_setup/4.

constraints

Returns a list of the problem constraints in denormalised (readable) form. They may be simplified with respect to the original set that was passed to lp_setup/4.

objective

Returns a term min(E) or max(E), representing objective function and optimisation direction. E is a linear expression.

method

Returns the method (default, primal, dual, net_primal, net_dual, barrier, barrier_primal, barrier_dual) that is used to solve the problem. In case of MIP solving, this is the start algorithm (the one that is used to solve the initial relaxation).

status

Status that was returned by the most recent invocation of the external solver.

cost

Cost of the current solution. Fails if no solution has been computed yet.

typed_solution

Returns a term ''(X1,...,Xn) whose arguments are the properly typed (integer or float) solution values for the corresponding problem variables (vars). The floating point solutions are the same as returned by solution, the integers are obtained by rounding the corresponding floating-point solution to the nearest integer. To instantiate the problem variables to their solutions, unify this term with the corresponding term containing the variables:

    instantiate_solution(Handle) :-
        lp_get(Handle, vars, Vars),
        lp_get(Handle, typed_solution, Values),
        Vars = Values.

slack

Returns a list of floating-point values representing the constraint slacks. The order corresponds to the list order in constraints. Fails if no solution has been computed yet.

dual_solution

Returns a list of floating-point values representing the dual solutions. The order corresponds to the list order in constraints. Fails if no solution has been computed yet.

demon_tolerance

Returns a comma-separated pair (RealTol,IntTol) of floating-point values which specify how far outside a variable's range an lp-solution can fall before lp_demon_setup/6 re-triggers. The tolerances differ for real (default 0.00001) and integer (default 0.5) variables.

simplex_iterations

Returns the external solver's count of simplex iterations.

node_count

Returns the external MIP solver's node count.

statistics

Returns a list of counter values [Successes, Failures, Aborts], indicating how often lp_solve/2 was invoked on the Handle, and how many invocations succeeded, failed and aborted respectively.

optimizer_param(Param)

Returns the value of the external solver's parameter Param for the problem represented by Handle. The external solver has a number of parameters that affect the way they work, and this queries their values. If Param is not a valid parameter for the solver, an out of range exception is raised. See below for more details on the parameters.

post_equality_when_unified

Returns the value (yes or no) if an equality constraint will be posted to a solver if two variables in the solver's problem are unified.

pool

Returns the name of the eplex instance (if any) associated with the solver state. Fails otherwise. Only useful if called with lp_get/3.

handle

Returns the solver state handle (if any) associated with the eplex instance. Fails otherwise. Only useful if called with eplex_get/2.

For the external solver's control parameter specified by optimizer_param(Param), Param must be an atom. The Value returned is either an integer, float or atom, depending on the parameter. The parameter is generally specific to a solver and version, and also, they may be problem specific, or global, again depending on the solver version. In all cases, the value returned by lp_get/3 is the current value for the parameter for the problem Handle. Refer to the solver documentation for details on the parameters. The names of the parameters are derived from the names of the parameters in the external solver. For CPLEX, take the parameter name from the CPLEX manual (or cplex.h), remove the CPX_PARAM_ prefix and convert the rest to lower case, e.g.

        CPX_PARAM_NODELIM becomes nodelim. 

	MAXNODE or XPRS_MAXNODE becomes maxnode. 

The following parameter names are additional aliases that work for either solver:

crash

CPX_PARAM_CRAIND (CPLEX) or XPRS_CRASH (XPRESS-MP) -integer

feasibility_tol

CPX_PARAM_EPRHS (CPLEX) or XPRS_FEASTOL (XPRESS-MP) - float

integrality

CPX_PARAM_EPINT (CPLEX) or XPRS_MIPTOL (XPRESS-MP) - float

iteration_limit

CPX_PARAM_ITLIM (CPLEX) or XPRS_LPITERLIMIT (XPRESS-MP) -integer

node_limit

CPX_PARAM_NODELIM (CPLEX) or XPRS_MAXNODE (XPRESS-MP) -integer

objdifference

CPX_PARAM_OBJDIF (CPLEX) or XPRS_MIPADDCUTOFF (XPRESS-MP) - float

refactor

CPX_PARAM_REINV (CPLEX) or XPRS_INVERTFREQ (XPRESS-MP) -integer

scrind

CPX_PARAM_SCRIND (CPLEX) or XPRS_OUTPUTLOG (XPRESS-MP) -integer

subalgorithm

CPX_PARAM_SUBALG (CPLEX) or XPRS_DEFAULTALG (XPRESS-MP) - integer

See Also