user_select_child

int user_select_child(void *user, double ub, branch_obj *can, char *action)

Description:

By the time this function is invoked, the candidate for branching has been chosen. Based on this information and the current best upper bound, the user has to decide what to do with each child. Possible actions for a child are KEEP_THIS_CHILD (the child will be kept at this LP for further processing, i.e., the process dives into that child), PRUNE_THIS_CHILD (the child will be pruned based on some problem specific property—no questions asked...), PRUNE_THIS_CHILD_FATHOMABLE (the child will be pruned based on its pre-solved LP relaxation) and RETURN_THIS_CHILD (the child will be sent back to tree manager). Note that at most one child can be kept at the current LP module.

There are two default options—in both of them, objective values of the pre-solved LP relaxations are compared (for those children whose pre-solve did not terminate with primal infeasibility or high cost). One rule prefers the child with the lowest objective function value and the other prefers the child with the higher objective function value.

Arguments:

void *user	IN	Pointer to the user-defined LP data structure.
int ub	IN	The current best upper bound.
branch_obj *can	IN	The branching candidate.
char *action	OUT	Array of actions for the children. The array is already allocated to length can->number.

Return values:

USER_ERROR	Error. DEFAULT is used.
USER_SUCCESS	User filled out *action.
USER_DEFAULT	Regulated by the select_child_default parameter, which is initially set to PREFER_LOWER_OBJ_VALUE, unless overridden by the user.
PREFER_HIGHER_OBJ_VALUE	Choose child with the highest objective value.
PREFER_LOWER_OBJ_VALUE	Choose child with the lowest objective value.
PREFER_MORE_FRACTIONAL	Choose child with the most fractional variables. Fractional branching options are only available if the fractional branching compile-time option is set in the makefile.
PREFER_LESS_FRACTIONAL	Choose child with the lowest number of fractional variables.

Post-processing:

Checks which children can be fathomed based on the objective value of their pre-solved LP relaxation.

Wrapper invoked from:

branch().