Search found 163 matches

by Fred
1 year ago
Forum: Modeling
Topic: Infeasible,no solution exist MIP using CPLEX
Replies: 5
Views: 1233

Re: Infeasible,no solution exist MIP using CPLEX

Munarita, I did not analyze your model in depth but your approach to try different formulations and check afterwards if results are satisfactory does not seem quite right to me. I think you should have a clear idea what you actually want to model and then verify your modeling approach by looking at ...
by Fred
1 year ago
Forum: Modeling
Topic: Low CPU utilization
Replies: 4
Views: 779

Re: Low CPU utilization

Hi, You can check in the lst file which equation is defined in line 94 and takes 2200 seconds to generate. Without knowing anything about the model (like e.g. #rows, #columns, #non-zeros) and that equation in particular, it is impossible to say how long it should take to generate. If you can share y...
by Fred
1 year ago
Forum: Modeling
Topic: Infeasible,no solution exist MIP using CPLEX
Replies: 5
Views: 1233

Re: Infeasible,no solution exist MIP using CPLEX

Munarita, A good idea, when implementing a new model is usually to look at the equation listing to make sure that you really modeled the equations properly. A frequent source of errors are for example lag and lead operators and that might be an issue in your model too. Looking for example at constra...
by Fred
1 year ago
Forum: Syntax
Topic: x^y, where x<0 and y non-integer
Replies: 3
Views: 945

Re: x^y, where x<0 and y non-integer

Hi Loreno,

The signPower function may be what you are looking for: https://www.gams.com/latest/docs/UG_Par ... =signpower

I hope this helps!

Best,
Fred
by Fred
1 year ago
Forum: Syntax
Topic: x^y, where x<0 and y non-integer
Replies: 3
Views: 945

Re: x^y, where x<0 and y non-integer

Loreno,

What you try to do is mathematically not defined.

Fred
by Fred
1 year ago
Forum: Solvers
Topic: Computational time of model extremely increased
Replies: 9
Views: 2976

Re: Computational time of model extremely increased

Peter, It seems that you try to set the mipemphasis option in your GAMS program. However, mipemphasis is a CPLEX solver option (https://www.gams.com/latest/docs/S_CPLEX.html#CPLEXmipemphasis) that needs to be specified via a solver option file and then you also need to instruct the solver to read th...
by Fred
2 years ago
Forum: Syntax
Topic: Unknown option (mipstart=1)
Replies: 2
Views: 985

Re: Unknown option (mipstart=1)

Hi, mipstart is not a GAMS but a solver option, see e.g. the CPLEX solver manual: https://www.gams.com/latest/docs/solvers/cplex/index.html#CPLEXmipstart Hence, mipstart needs to be set in a solver option file: https://www.gams.com/latest/docs/solvers/introduction/index.html#BASIC_USAGE_SOLVER_OPTIO...
by Fred
2 years ago
Forum: Tools
Topic: Convert Gams files to *.mpi or *.mps
Replies: 4
Views: 2057

Re: Convert Gams files to *.mpi or *.mps

Hi Masood, The example below is based on the well known transportation problem from the GAMS model library (https://www.gams.com/latest/gamslib_ml/libhtml/gamslib_trnsport.html) and illustrates how to create an MPS file using Convert. Sets i canning plants / seattle, san-diego / j markets / new-york...
by Fred
2 years ago
Forum: Modeling
Topic: Model "infeasible"
Replies: 4
Views: 2188

Re: Model "infeasible"

Hi Ping,

the ++ is a "Circular Lag and Lead Operator". A detailed description of lag and lead operators for ordered sets can be found in the documentation: https://gams.com/latest/docs/userguides ... dOperators

Best,
Fred
by Fred
2 years ago
Forum: Modeling
Topic: Model "infeasible"
Replies: 4
Views: 2188

Re: Model "infeasible"

Hi grideman, your formulation of equation temparature(t) is problematic. For the last t=9 you refer to temp(t+1) on the right hand side which doesn't exist. There are different workaraounds for that. Either you may want to link your last time step to the first one and use t++1 (this may still be har...