Which solver to use with vSPD?

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Last post 30 October 2018

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Phil Bishop posted this 02 August 2016 - Last edited 21 September 2017

When purchasing a GAMS system it is necessary to choose one or more solvers. We are often asked what is the best solver to use for models such as vSPD and GEM?

vSPD is generally formulated as a linear programming (LP) model but under certain conditions it might be a mixed integer programming (MIP) problem. An LP/MIP solver is then clearly required. To state the obvious, the first consideration is that the solver to choose must be available with GAMS, as vSPD and GEM are GAMS-based models. There are many solvers to choose from and the Authority doesn't really endorse any particular one. That said, we have in the past trialled Gurobi, Cplex and Xpress - and all three of those solvers worked well with both vSPD and GEM. While we have never trialled Mosek, we understand that it too is an adequate solver.

GEM is frequently configured to be a very large MIP problem. A solver that performs well on MIPs should be selected if GEM is going to be the predominant model to be solved.

A test license with a limited life can be arranged if you want to try several solvers before making a decision.

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Tuong Nguyen posted this 06 September 2016 - Last edited 11 September 2016

vSPD is set to use Cplex by default because the Authority uses Cplex. In order to use a different solver, users need to edit the 'Solver' global control variable accordingly. This variable is declared and initialised in "..\Programs\vSPDsettings.inc", a text file:

$setglobal Solver Cplex (Default)

$setglobal Solver Xpress

$setglobal Solver Gurobi

$setglobal Solver Mosek

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Phil Bishop posted this 13 September 2016

In vSPD, the global control variable called ‘Solver’ performs no role apart from telling GAMS what solver to use. This is not necessarily the case with other models such as GEM, where we also use the ‘Solver’ variable to create and name a solver-specific options file. A solver options file enables us to change some of the default settings for the solver so that the solver performs better.

If you run into problems when you modify the ‘Solver’ control variable, please use the forum to post the relevant .lst file containing the message associated with the first error you encounter. The more relevant information you provide, the more likely it is that somebody can assist you. If you simply announce that ‘the model won’t solve’, there’s not really much that anybody can do to help.

Authority staff may be able to assist but our experience with solvers other than Cplex is very limited. It is more likely that somebody out there using the same solver as you will be able to help.

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quincy posted this 30 October 2018

When purchasing a GAMS system it is necessary to choose one or more solvers. We are often asked what is the best solver to use for models such as vSPD and GEM?

vSPD is generally formulated as a linear programming (LP) model but under certain conditions it might be a mixed integer programming (MIP) problem. An LP/MIP solver is then clearly required. To state the obvious, the first consideration is that the solver to choose must be available with GAMS, as vSPD and GEM are GAMS-based models. There are many solvers to choose from and the Authority doesn't really endorse any particular one. That said, we have in the past trialled Gurobi, Cplex and Xpress - and all three of those solvers worked well with both vSPD and GEM. While we have never trialled Mosek, we understand that it too is an adequate solver.

GEM is frequently configured to be a very large MIP problem. A solver that performs well on MIPs should be selected if GEM is going to be the predominant model to be solved.

A test license with a limited life can be arranged if you want to try several solvers before making a decision.

Hi there, I am interested in using vSPD and the online version does not suit my needs. Purchacing a GAMS lisence is quite costly as I dont know yet if it is even possible to model the scenarios I desire (Future outputs with changing demand/supply etc). You mentioned above that a test license is available. Is this something you still offer?

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Phil Bishop posted this 30 October 2018 - Last edited 13 February 2020

You will need to contact the GAMS sales folk to request an evaluation license for GAMS. If it's vSPD you're looking to evaluate, be sure to tell them you're interested in evaluating a model that is a large LP/MIP problem.

If they issue you with an evaluation license, it will probably be good for 30 days. So make sure you are ready to actually start testing before you make your request, i.e. download and install an unlicensed copy of GAMS and test that you can edit and solve a small model from the GAMS model library. Also download and unpack vSPD and make sure you understand what the various codes in the vSPD model system are and how they relate to each other. The vSPD codes are just text files. You will not be able to solve vSPD with an unlicensed version of the GAMS software, but you can use the GAMS IDE, or the GAMS Studio, to explore the codes that comprise the vSPD model. You can also the IDE or Studio to examine a GDX file for vSPD.

Which solver to use with vSPD?

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