Accessing external software tools

GAMS
1

Hello,

we are thinking about using GAMS for our work. Therefore we need to know whether there is some interface to access data evaluated by an external tool.

We have a system for thermodynamic properties, that can return for example the value (not the function) of the temperature of a mixture at a given pressure. Finding the optimum temperature could be our modelling task. So, is it possible to declare temperature and pressure as variables, that are evaluated the described way? If it is possible, do we need to provide derivative information, too?

Many thanks in advance,
Andreas

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2

HI Andreas



Gams has lots of possibilities to access data from other software. See the information on

  •      Gdxxrw (Excel)

  •      Gdxrrw (R Statistics)

Moreover, there are several APIs (for example for Python).



Cheers

Renger



Von: gamsworld@googlegroups.com [mailto:gamsworld@googlegroups.com] Im Auftrag von Andreas
Gesendet: Montag, 29. Juni 2015 09:16
An: gamsworld@googlegroups.com
Betreff: Accessing external software tools



Hello,



we are thinking about using GAMS for our work. Therefore we need to know whether there is some interface to access data evaluated by an external tool.



We have a system for thermodynamic properties, that can return for example the value (not the function) of the temperature of a mixture at a given pressure. Finding the optimum temperature could be our modelling task. So, is it possible to declare temperature and pressure as variables, that are evaluated the described way? If it is possible, do we need to provide derivative information, too?



Many thanks in advance,

Andreas

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3

Andreas,

Sounds like you want to use a function relating temperature and pressure in an optimization, not just to compute data values in a table. That’s a crucial detail.

Assuming you want to use a function in a GAMS model, but you can’t implement the function in GAMS algebra, I can suggest to options. The best is to implement the function as a GAMS extrinsic. This assumes the function has a small number of inputs: currently I believe the limit is 10 but we might have adjusted that. Once you’ve done the implementation, you can use the function exactly as you’d use any GAMS intrinsic like sin(), exp(), arctan2(x,y), etc. For more info, see

http://www.gams.com/mccarl/mccarlhtml/extrinsic_functions.htm

If your function has more variables than are allowed by extrinsic functions, or otherwise doesn’t work as an extrinsic, you can use the external equation capability of GAMS. Here’s a good link comparing the two approaches.

http://support.gams.com/doku.php?id=gams:extrinsic_function_vs._external_equation

-Steve


On Mon, Jun 29, 2015 at 3:15 AM, Andreas wrote:

Hello,

we are thinking about using GAMS for our work. Therefore we need to know whether there is some interface to access data evaluated by an external tool.

We have a system for thermodynamic properties, that can return for example the value (not the function) of the temperature of a mixture at a given pressure. Finding the optimum temperature could be our modelling task. So, is it possible to declare temperature and pressure as variables, that are evaluated the described way? If it is possible, do we need to provide derivative information, too?

Many thanks in advance,
Andreas

–
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\

Steven Dirkse, Ph.D.
GAMS Development Corp., Washington DC
Voice: (202)342-0180 Fax: (202)342-0181
sdirkse@gams.com
http://www.gams.com

4

That was the crucial detail I was pointing on.
Thanks a lot for your answer!!



Am Montag, 29. Juni 2015 09:17:46 UTC+2 schrieb Andreas:

Hello,

we are thinking about using GAMS for our work. Therefore we need to know whether there is some interface to access data evaluated by an external tool.

We have a system for thermodynamic properties, that can return for example the value (not the function) of the temperature of a mixture at a given pressure. Finding the optimum temperature could be our modelling task. So, is it possible to declare temperature and pressure as variables, that are evaluated the described way? If it is possible, do we need to provide derivative information, too?

Many thanks in advance,
Andreas

–
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