[BCP] Antw: pruning node after integral feasible solution is found ?

[Andrea Trautsamwieser]

Dear Changhyeok,
 
do you know the lower bound LB of your problem? Usually, the node is
fathomed if the LB >= UB. Otherwise, the method
"select_branching_candidates()" is looking for branching candidates and
in case no variable is found reports the error you've got.
 
For short, you can also fathom the node with 
 
BCP_DoNotBranch_Fathomed 
 
in your own "select_branching_candidates()" method.
 
Hope this helps,
 
Andrea



>>> Changhyeok Lee <changhyeoklee at gmail.com> 11.12.2012 01:43 >>>
Hello,  

I'm trying to solve an MILP using BCP package. Currently my problem has
only core variable and constraints (no indexed cuts or variables to
add).  

I'm using Clp solver and I have implemented the Gomory cuts using
CglGomory library within "generate_cut_in_lp" and "cut_to_row"
function.

For my current test problem, the output log contains the following
messages.

LP: **** Processing NODE 0 on LEVEL 0 (from TM) ****

….

LP: **** Processing NODE 1 on LEVEL 1 (dived) ****

….

LP: **** Processing NODE 3 on LEVEL 2 (dived) ****

In the first iteration of the last NODE 3, the Clp finds an integral
solution and it prints the following output.

LP: Default test_feasibility() executed.
LP: Default test_full() executed.
LP: Default pack_feasible_solution() executed.
TM: Default unpack_feasible_solution() executed.
TM: Solution found at 1.793 sec.
TM 5.885: Sol from proc: 1 val: -3.320268 (prev best: infinity) tree
size/procd: 5/2 cand list ins/size: 3/4



Then, it continues the LP process and finally I see the following error
message.

LP: Default select_branching_candidates() executed.
BM: Couldn't branch!



Here is my question. How do we prune the node after I find an integral
solution?  

My understanding is that in the branch and bound process, if we find an
integral solution, then we just update the best incumbent solution and
prune the node. However, it seems that my code continues to work on the
node and even try to branch. Obviously, there's nothing to branch (all
integral solution) and the BCP package generates the error message.

Am I missing something? What do I need to do to have my BCP code to
prune the integral node?

Thank you in advance for your help!

----
Changhyeok




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