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## Re: [Help-glpk] [Fwd: Depth first search]

**From**: |
Andrew Makhorin |

**Subject**: |
Re: [Help-glpk] [Fwd: Depth first search] |

**Date**: |
Thu, 21 Apr 2011 17:22:28 +0400 |

>* In order to get a feasible integer solution fast I use depth first*
>* search.*
>* Since I have constraints of the type Sum_i (x_i) = 1, x_i >= 0, I would*
>* like to branch up in the search. Does GLPK always branch down in the*
>* depth first search? (In that case I can replace variable x_i by 1 - x_i*
>* in order to simulate a branch up in the depth first search.)*
>* *
It depends on which (down- or up-) branch seems to be stronger, that, in
turn, depends on the branching heuristic used. For example, if the
branching on most fractional variable (--mostf) and depth first search
(--dfs) are used, the branch to be solved next is that one, where
integer infeasibility of the branching variable is less than in other
one.
You may change the default behavior either by providing your own
heuristic in the callback function or by changing appropriate glpk
routine (see file src/glpios09.c).