[SCIP] No branching on solving NLP (number of nodes remains eq. to 1)

[Benjamin Müller]

Dear Vladimir,

yes, SCIP did not start to branch yet. Due to the large number of 
generated cutting planes, I would suspect that most of the time is spent 
in solving the LP relaxations, but it could also be that some plugins 
are too expensive. You could print the statistics and check which 
plugins could be disabled/configured to improve SCIP's performance.

Could you send me your instance in the CIP format? Then I could have a 
look at your instance.

Best regards,
Benjamin

On 10/8/19 10:11 AM, Vladimir V. Voloshinov wrote:
> Dear SCIP developers,
> we tried to solve some "middle-size" nonlinear problem with polynomial 
> functions in constraints with out any discrete variables (extr. from 
> NL-file header below)
>   430 442 1 0 401 # vars, constraints, objectives, ranges, eqns
>   199 1 0 0 0 0      # nonlinear constrs, objs; ccons: lin, nonlin, nd, nzlb
>   129 221 26         # nonlinear vars in constraints, objectives, both
>    0 0 0 0 0             # discrete variables: binary, integer, 
> nonlinear (b,c,o)
> Some of nonlinear constraints are non-convex quadratic and others (100 
> totally) are 3rd order polynomial, i.e. sums of the items like " 
> <var1>*sqr(<var2>)"  (in CIP format).
> Local solver IPOPT founds local optimum (we suspect that it is global) 
> in 10 seconds.
> But SCIP with default settings (and FiberSCIP) can not prove global 
> optimality in an hours and I DO NOT SEE ANY BRANCHING (domain 
> decomposition), see fragment of SCIP-log:
> =============================
>   time | node  | left  |LP iter    |LP it/n| mem |mdpt |frac |vars |cons 
> |cols |rows |cuts   | ,,, | dualbound       | primalbound  |  gap
>   5004s|     1 |     0   | 12932k|     -      |  77M|   0     |   0  | 
> 427 | 438 | 427 |  89k | 190k | ... |-2.167723e-01 | 1.615240e-01 |    Inf
> ...........
>    358m|     1 |     0   | 31028k|     -     | 103M|   0    |   0   | 
> 427 | 438 | 427 | 126k| 259k| ...  |-1.800902e-01 | 1.615240e-01 |    Inf
> SCIP Status        : solving was interrupted [user interrupt]
> Solving Time (sec) : 21469.69
> Solving Nodes      : 1
> Primal Bound       : +1.61523993625950e-01 (2 solutions)
> Dual Bound         : -1.80090245701914e-01
> =============================
> 
> I understand that it is a hard problem, but it is strange that solver 
> did not try to split bounded domain ! Only number of linear cuts has 
> been increasing...
> It looks like SCIP only tries to approximate objective function epigraph 
> by polyhedron (as a result lower bound increases slowly).
> 
> Is it normal behaviour of SCIP or some settings for branching rules may 
> be applied ?
> 
> Sincerely yours,
> -- 
> Vladimir V. Voloshinov,
> Ph.D, head of lab. C-3 "Distributed computing algorithms", 
> http://www.iitp.ru/ru/researchlabs/1040.htm,
> Center for Distributed Computing, Institute for Information Transmission 
> Problems RAS, http://www.iitp.ru
> web: our site is temporarily offline 
> <https://scholar.google.ru/citations?hl=en&user=-m4QhNEAAAAJ&view_op=list_works&sortby=pubdate>
> 
> _______________________________________________
> Scip mailing list
> Scip at zib.de
> https://listserv.zib.de/mailman/listinfo/scip
> 

-- 
______________________________
Benjamin Müller
Zuse Institute Berlin
Takustr. 7, 14195 Berlin
benjamin.mueller at zib.de
+49 30 841 85-195