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EplexInstance:eplex_set(++ParamName, -Value)

Change initial options for solver state associated with EplexInstance
ParamName
Name of parameter (atom)
Value
New value for ParamName

Description

This primitive can be used to change some of the initial options even after setup of a solver for eplex instance EplexInstance. What can be one of the following:

method
Set the method that will be used to solve the problem. Value is one of default, primal, dual, net, net(Simplex), barrier, barrier(Crossover), sifting, sifting(SubMethod). Simplex can be one of default, primal, dual, specifying the Simplex method to use in the Network Simplex algorithm. Crossover can be one of default, primal, dual, none, specifying the crossover method to use for the barrier method. SubMethod could be one of default, primal, dual, net, barrier, specifying the method to use for the subproblems in the sifting method. Note that some of these methods may not be available on all external solvers. In case of MIP solving, this is the start algorithm (the one that is used to solve the initial relaxation).

node_method
Applicable to MIP problems only. Set the method that will be used to solve the problem at the nodes (except the root) of the branch-and-bound tree. Note that the method for solving the root node is controlled by the method option. Value can be set to the same values as in the method option, although there may be more restrictions on what the actual methods/auxiliary methods that are allowed in combination with the root method, due to limitations/restrictions from the external solver. A warning will be given when the problem is solved if this is the case, and the default method used instead.

solution
Make the solutions available each time the problem has been (re-)solved successfully. Value is one of the atoms yes or no.

reduced_cost
Make the reduced costs available each time the problem has been (re-)solved successfully. If the problem is a MIP, then depending on the external solver, this is either unavailable or are the values for the optimal LP node. Value is one of the atoms yes or no.

slack
Make the constraint slacks available each time the problem has been (re-)solved successfully. Value is one of the atoms yes or no.

dual_solution
Make the dual solutions available each time the problem has been (re-)solved successfully. If the problem is a MIP, then depending on the external solver, this is either unavailable or are the values for the optimal LP node. Value is one of the atoms yes or no.

keep_basis
Store the basis each time the problem has been solved successfully, and use this basis as a starting point for re-solving next time. Value is one of the atoms yes or no.

cache_iis
When a problem is found to be infeasible, compute an IIS for the problem (if supported by the external solver), and store it so that it can bee retrieved by eplex_get_iis/4 or lp_get_iis/5. This will be done before the problem can be modified and make the computing of the IIS impossible. The IIS will only be available before the problem is solved again, and before the infeasible solve is backtracked. This option has no effect if the external solver does not support the finding of IIS. Note that if this option is set, eplex will always ask for an IIS to computed for an infeasible problem, even if it is immediately backtracked by the infeasible handler failing, and that the option is only needed if the problem instance in the external solver is modified before eplex_get_iis/4 or lp_get_iis/5 is called. Value is one of the atoms yes or no.

demon_tolerance
Specify how far outside a variable's range an lp-solution can fall before lp_demon_setup/5 re-triggers. Value is a comma-separated pair (RealTol,IntTol) of floating-point values (default (0.00001,0.5)).

use_var_names
Specify if variable names (set using set_var_name/2 of the var_name library) should be passed to the external solver. If a particular variable does not have a name, a solver's default name would be used. Note that for XPRESS-MP, there is a limit on the length of the name, which can be changed between 8 and 64 in steps of 8 with the parameter N_NAMLEN. Variable names longer than this limit are truncated to the limit. Note also that only new variables from constraints added after the lp_set/3 call will pass their names to the external solver. Value is one of the atoms yes or no.

timeout
Set the external solver to time-out after Value seconds. The solver will abort (in either the abort or suboptimal state, depending on if a suboptimal solution was found) if the optimal solution was not found within the time limit. In cases where the solver expects an integer for the time-out interval, the time given is rounded up to the next integer value. This should be used instead of the solver specific optimizer_param(Param) for setting timeouts, as eplex sets these parameter(s) itself. Note that the exact behaviour of the timeout setting is solver dependent. Value is a positive number.

suboptimal_handler
Value is a user defined goal to handle the case when the external solver returned a suboptimal solution (because the problem was aborted). Value would replace any existing suboptimal handler, and would also be run in place of raising the default eplex_suboptimal event.

unbounded_handler
Value is a user defined goal to handle the case when the problem is unbounded. Value would replace any existing unbounded handler, and would be run in place of raising the default eplex_unbounded event.

infeasible_handler
Value is a user defined goal to handle the case when the external solver found the problem to be infeasible. Value would replace any existing infeasible handler, and would be run in place of raising the default eplex_infeasible event. Note that the default and logically correct behaviour is to fail, this handler is provided to allow the user to analyse the cause of the infeasibility. It is recommended that the handler should also fail after performing the analysis.

unknown_handler
Value is a user defined goal to handle the case when the external solver was not able to determine if the problem is unbounded Value would replace any existing unknown handler, and would be run in place of raising the default eplex_unknown event.

abort_handler
Value is a user defined goal to handle the case when the external solver aborted without finding any solution. Value would replace any existing abort handler, and would be run in place of raising the default eplex_abort event.

optimizer_param(Param)
Set the external solver's control parameter Param for the problem Handle. If the solver's parameters are global and not problem specific, an unimplemented functionality exception would be raised. See lp_get/3 for more details on the external solver's parameters. Note that the new setting is not undone on backtracking.

write_before_solve
Value can be the pair (Format,File) or the atom no. If (Format,File) is given, Eplex will ask the external solver to dump the problem each time the solver is solved. This allows the problem in an eplex_probe/2 or lp_probe/3 to be dumped. As in lp_write/3, Format is the format of the dumped problem, and File is the filename. See for more details. Note that the problem is dumped each time the external solver is invoked if the problem has cutpool constraints, where there may be multiple invocations of the solver per solver call. `no' for Value will turn off this dumping.

post_equality_when_unified
Value can be the atoms yes or no. Determines if an equality constraint will be posted to a solver when two of its variables are unified. Setting Value to no means that the constraint will not be posted. Note that this could mean that the solver's problem may become inconsistent with ECLiPSe's.

Making solutions available means that they can be retrieved using lp_get/3 or lp_var_get/4 after the solver has been run successfully.

Resatisfiable

no

Exceptions

(5) type error
EplexInstance does not a solver setup for it.
(40) stale object handle
Solver state had been previously destroyed.

See Also

eplex_solver_setup / 4, eplex_set / 2, eplex_get_iis / 4, lp_set / 3, lp_get / 3