int user_select_child(void *user, double ub, branch_obj *can, char *action)
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.
|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.|
|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.|
Checks which children can be fathomed based on the objective value of their pre-solved LP relaxation.