
lp_set(+Handle, ++What, +Value)

   Change initial options for solver state Handle.

Arguments
   Handle              Handle to a solver state
   What                Option to set
   Value               Value being set

Type
   library(eplex)

Description

This primitive can be used to change some of the initial options
even after setup. 
Handle refers to an existing solver state,
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.


    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.

    cutpool_option(Idx,Option)
        Set the option Option as specified by Value for the cutpool
        constraint with index Idx. Option is one of the following:

           active
               Set the active status for the constraint Idx to Value.
                   Value can be 0 or 1. 0 is non-active, 1 is active.
           add_initially
               Specify if the constraint Idx should be added to a
                   problem before the solver is invoked. 
                   Value can be 0 or 1. 1 is to add initially, 0 not.


        Note that the option is not undone on
        backtracking.

    cutpool_group
        Value is an atom, and is used to specify the name of a group of
        cutpool constraints. If Name is not a current group name, a new
        group with that name is created. Once created, a named group exists
        until the problem is destroyed. The default group (with the atom
        nil ([]) as its name) is predefined and does not need to
        be created with cutpool_group.

    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.

    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. 

    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 between two solver variables will be posted to the
        solver when these variables are unified. Setting Value to no means
        that the constraint will not be posted. Note that this can
        lead to the solver's problem becoming 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

See Also
   lp_setup / 4, lp_get / 3, lp_var_get / 4, eplex_set / 2
