XPRS_bo_create

Purpose

Creates a new user defined branching object for the Optimizer to branch on. This function should be called only from within one of the callback functions set by XPRSaddcboptnode, XPRSaddcbchgbranchobject, or XPRSaddcbpreintsol (only if the soltype is 0).

Topic area

Branching Object

Synopsis

int XPRS_CC XPRS_bo_create(XPRSbranchobject* p_bo, XPRSprob prob, int isoriginal);

Arguments

p_bo

Pointer to where the new object should be returned.

prob

The problem structure that the branching object should be created for.

isoriginal

If the branching object will be set up for the original matrix, which determines how column indices are interpreted when adding bounds and rows to the object:

0	Column indices should refer to the current (presolved) node problem.
1	Column indices should refer to the original matrix.

Example

The following function will create a branching object equivalent to a standard binary branch on a column:

XPRSbranchobject CreateBinaryBranchObject(XPRSprob xp_mip, int icol)
{
  char   cBndType;
  double dBndValue;
  int isoriginal = 1;

  XPRSbranchobject bo = NULL;

  /* Create the new object with two empty branches. */
  XPRS_bo_create(&bo, xp_mip, isoriginal);
  XPRS_bo_addbranches(bo, 2);

  /* Add bounds to branch the column to either zero or one. */
  cBndType = 'U';
  dBndValue = 0.0;
  XPRS_bo_addbounds(bo, 0, 1, &cBndType, &icol, &dBndValue);
  cBndType = 'L';
  dBndValue = 1.0;
  XPRS_bo_addbounds(bo, 1, 1, &cBndType, &icol, &dBndValue);

  /* Set a low priority value so our branch object is picked up */
  /* before the default branch candidates. */
  XPRS_bo_setpriority(bo, 100);

  return bo;
}

See also example mostviolated.c.

Further information

1. In addition to the standard MIP entities supported by the Optimizer, the Optimizer also allows the user to define their own entities for branching, using branching objects.

2. A branching object of type XPRSbranchobject should provide a linear description of how to branch on the current node for a user's entities. Any number of branches is allowed and each branch description can contain any combination of columns bounds and new constraints.

3. Branching objects must always contain at least one branch and all branches of the object must contain at least one bound or constraint.

4. If multiple lower or multiple upper bounds on the same variable are given, the strictest one will be applied.

5. When the Optimizer branches the current node on a user's branching object, a new child node will be created for each branch defined in the object. The child nodes will inherit the bounds and constraint of the current node, plus any new bounds or constraints defined for that branch in the object.

6. Inside the callback function set by XPRSaddcboptnode, a user can define any number of branching objects and pass them to the Optimizer. These objects are added to the set of infeasible entities for the current node and the Optimizer will select a best candidate from this extended set using all of its normal evaluation methods.

7. The callback function set by XPRSaddcbchgbranchobject can be used to override the Optimizer's selected branching candidate with the user's own object. This can for example be used to modify how to branch on the MIP entity selected by the Optimizer.

8. The following functions are available to set up a new user branching object:

XPRS_bo_create	Creates a new, empty branching object with no branches.
XPRS_bo_addbranches	Adds new, empty branches to the object. Branches must be created before column bounds or rows can be added to a branch.
XPRS_bo_addbounds	Adds new column bounds to a given branch of the object.
XPRS_bo_addrows	Adds new constraints to a given branch of the object.
XPRS_bo_setpriority	Sets the priority value for the object. These are equivalent to the priority values for regular MIP entities that can be set through directives (see also Appendix The Directives (.dir) File).
XPRS_bo_setpreferredbranch	Specifies which of the child nodes corresponding to the branches of the object should be explored first.
XPRS_bo_store	Adds the created object to the candidate list for branching.

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XPRS_bo_create