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## Re: [Help-glpk] Sets of ordered pairs: Differences between AMPL and GNU

 From: xypron Subject: Re: [Help-glpk] Sets of ordered pairs: Differences between AMPL and GNU MathProg Date: Tue, 18 Nov 2008 11:53:29 -0800 (PST)

```Hello Andrew,

64bit Windows Server 2003 with the 64bit glpsol executable available as
glpsol-4.33_64bit.zip  at
http://winglpk.sourceforge.net http://winglpk.sourceforge.net
also gives:
Minimize
z: + X(1,b2) + 2 X(1,b3) + X(1,b5)

Best regards

Xypron

xypron wrote:
>
> Hello Andrew,
>
> on a i386 Ubuntu with glpk-4.33
> ./glpsol -m test1.mod --check --wcpxlp test.clp
> resulted in:
>
> \* Problem: test1 *\
>
> Minimize
>  z: + X(1,b2) + 2 X(1,b3) + X(1,b5)
>
> Subject To
>
> Bounds
>  X(1,b2) free
>  X(1,b3) free
>  X(1,b5) free
>
> End
>
> Best regards
>
> Xypron
>
>
> Peter Ingerfeld-2 wrote:
>>
>> There is an inhomogeneity between AMPL and MathProg in the way sets of
>> ordered pairs are being iterated over by two (or more) sum{} statements
>> which are linked by an iterator variable.
>>
>> Consider the following sample:
>> ---------------------------
>>
>> set A :={1..5};
>> set B :={"b1", "b2", "b3", "b4", "b5"};
>>
>> set D within {A,B} := {(1,"b2"), (1,"b3"), (1,"b5"), (3,"b3")};
>>
>> var X {D};
>>
>> minimize z:
>>  sum{a in (1..5)} sum {(a,b) in D} X[1,b];
>>
>> ---------------------------
>>
>> AMPL generates:
>>
>> MIN   X[1,b2] + 2 X[1,b3] + X[1,b5]
>>
>> MathProg generates:
>>
>> MIN   5 X[1,b2] + 5 X[1,b3] + 5 X[1,b5]
>>
>> Obviously AMPL links the inner and outer sum{} statements by variable 'a'
>> and MathProg doesn't.
>>
>> Bug or feature?
>>
>> Dr. Peter Ingerfeld
>> MOPS Optimierungssysteme GmbH & Co KG
>>
>>
>>
>>
>>
>>
>> _______________________________________________
>> Help-glpk mailing list
>> http://lists.gnu.org/mailman/listinfo/help-glpk
>>
>>
>
>

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