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XPRSreaddirs

READDIRS

Purpose

Reads a directives file to help direct the global search.

Synopsis

int XPRS_CC XPRSreaddirs(XPRSprob prob, const char *filename);

READDIRS [filename]

Arguments

prob	The current problem.
filename	A string of up to 200 characters containing the file name from which the directives are to be read. If omitted (or NULL), the default problem_name is used with a .dir extension.

Related Controls

Double

PSEUDOCOST  
                     

Default pseudo cost in node degradation estimation.

Example 1 (Library)

The following example reads in directives from the file sue.dir for use with the problem, steve:

XPRSreadprob(prob,"steve","");
XPRSreaddirs(prob,"sue");
XPRSminim(prob,"g");

Example 2 (Console)

READPROB
READDIRS
MINIM -g

This is the most usual form at the console. It will attempt to read in a directives file with the current problem name and an extension of .dir.

Further information

1. Directives cannot be read in after a model has been presolved, so unless presolve has been disabled by setting PRESOLVE to 0, this command must be issued before XPRSmaxim (MAXIM) or XPRSminim (MINIM).

2. Directives can be given relating to priorities, forced branching directions, pseudo costs and model cuts. There is a priority value associated with each global entity. The lower the number, the more likely the entity is to be selected for branching; the higher, the less likely. By default, all global entities have a priority value of 500 which can be altered with a priority entry in the directives file. In general, it is advantageous for the entity's priority to reflect its relative importance in the model. Priority entries with values in excess of 1000 are illegal and are ignored. A full description of the directives file format may be found in The Directives (.dir) File.

3. By default, XPRSglobal (GLOBAL) will explore the branch expected to yield the best integer solution from each node, irrespective of whether this forces the global entity up or down. This can be overridden with an UP or DN entry in the directives file, which forces XPRSglobal (GLOBAL) to branch up first or down first on the specified entity.

4. Pseudo-costs are estimates of the unit cost of forcing an entity up or down. By default XPRSglobal (GLOBAL) uses dual information to calculate estimates of the unit up and down costs and these are added to the default pseudo costs which are set to the PSEUDOCOST control. The default pseudo costs can be overridden by a PU or PD entry in the directives file.

5. If model cuts are used, then the specified constraints are removed from the matrix and added to the Optimizer cut pool, and only put back in the matrix when they are violated by an LP solution at one of the nodes in the global search.

6. If creating a directives file by hand, wild cards can be used to specify several vectors at once, for example PR x1* 2 will give all global entities whose names start with x1 a priority of 2.