basic question (ilogical?)

GAMS
1

Hello Everybody,

I really need some help understanding how GAMS works, because I get an error message which I can’t understand at all!

I did the basic transportation example to understand gams better (http://de.wikipedia.org/wiki/General_Algebraic_Modeling_System) and guess what: I did the example the exact same way, but at the beginning I changed the orden of the set values.

So instead of: i canning plants / seattle, san-diego /
I put: i canning plants / san-diego, seattle /

and this changed the solution of the problem. Can someone please tell me what the f is going on? Even if you change the orden aswell in the a-parameter and the table (so it would be first san-diego, than seattle), it doesn’t work! Shouldn’t it be the same solution???

I’d really appreciate it, if someone could explain this to me!
Thanks in advance, Jens

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2

Hi Jens



The trnsport.gms model has alternate optimal solutions, i.e. the solution is not unique. The objective function value is the same in these solutions, but the value of the variables is not.



Regards



Arne


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Arne Stolbjerg Drud

ARKI Consulting & Development A/S

Bagsvaerdvej 246A, DK-2880 Bagsvaerd, Denmark

Phone: (+45) 44 49 03 23, Fax: (+45) 44 49 03 33, email: adrud@arki.dk



From: gamsworld@googlegroups.com [mailto:gamsworld@googlegroups.com] On Behalf Of dondiiionys@gmail.com
Sent: Monday, June 17, 2013 6:55 PM
To: gamsworld@googlegroups.com
Subject: basic question (ilogical?)



Hello Everybody,

I really need some help understanding how GAMS works, because I get an error message which I can’t understand at all!

I did the basic transportation example to understand gams better (http://de.wikipedia.org/wiki/General_Algebraic_Modeling_System) and guess what: I did the example the exact same way, but at the beginning I changed the orden of the set values.

So instead of: i canning plants / seattle, san-diego /
I put: i canning plants / san-diego, seattle /

and this changed the solution of the problem. Can someone please tell me what the f is going on? Even if you change the orden aswell in the a-parameter and the table (so it would be first san-diego, than seattle), it doesn’t work! Shouldn’t it be the same solution???

I’d really appreciate it, if someone could explain this to me!
Thanks in advance, Jens

–
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To post to this group, send email to gamsworld@googlegroups.com.
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For more options, visit https://groups.google.com/groups/opt_out.


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3

thank you sooooo much!!!

Am Montag, 17. Juni 2013 11:55:14 UTC-5 schrieb dondi...@gmail.com:

Hello Everybody,

I really need some help understanding how GAMS works, because I get an error message which I can’t understand at all!

I did the basic transportation example to understand gams better (http://de.wikipedia.org/wiki/General_Algebraic_Modeling_System) and guess what: I did the example the exact same way, but at the beginning I changed the orden of the set values.

So instead of: i canning plants / seattle, san-diego /
I put: i canning plants / san-diego, seattle /

and this changed the solution of the problem. Can someone please tell me what the f is going on? Even if you change the orden aswell in the a-parameter and the table (so it would be first san-diego, than seattle), it doesn’t work! Shouldn’t it be the same solution???

I’d really appreciate it, if someone could explain this to me!
Thanks in advance, Jens

–
To unsubscribe from this group and stop receiving emails from it, send an email to gamsworld+unsubscribe@googlegroups.com.
To post to this group, send email to gamsworld@googlegroups.com.
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For more options, visit https://groups.google.com/groups/opt_out.

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