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RE: next question - find some element of a set
From: |
Meketon, Marc |
Subject: |
RE: next question - find some element of a set |
Date: |
Thu, 12 Dec 2019 18:12:18 +0000 |
Thank you. That works in the case that the array cost is numeric (and would
work for me in this case!).
The max function will not work if the array is symbolic. Out of sheer
curiosity, I wonder if there is a general solution for getting an element from
a set and putting that into a (symbolic) parameter.
-----Original Message-----
From: Mate Hegyhati <address@hidden>
Sent: Thursday, December 12, 2019 12:35 PM
To: Meketon, Marc <address@hidden>; address@hidden
Subject: Re: next question - find some element of a set
Hi!
Thanks for the clarification. If I understand correctly, and ANY proper cost
value is ok, and you don't need the element itself, just the cost value, then
min/max could also work.
param some_valid_cost := max{s in S} cost[s];
Another more "random" solution (more like a workaround):
param selector{s in S} := Irand224();
param some_valid_cost := sum{s in S: selector[s] == max {ss in S} selector[ss]}
cost[s];
(but it fails, if the max value is generated twice)
I hope this helps.
All the best!
Mate
On 12/12/19 4:19 PM, Meketon, Marc wrote:
> Here is more clarification. I have a set S and an array cost[].
> I wanted to get a cost -- any cost -- that is found in the array cost.
> I didn't want to have to specify in the data section a sample element
> of S, I just wanted to use GMPL to find one. In the example below, I
> want to find SOME_ELEMENT_IN_S as an index to the array cost[].
>
> set S; param cost{S};
>
> param some_valid_cost := cost[SOME_ELEMENT_IN_S];
>
> data; param : S : cost := A 100 B 105 C 198 ;
>
> -----Original Message----- From: Help-glpk
> <help-glpk-bounces+marc.meketon=address@hidden> On Behalf Of
> Mate Hegyhati Sent: Thursday, December 12, 2019 2:29 AM To:
> address@hidden Subject: Re: next question - find some element of a
> set
>
> Hi!
>
> I'm not exactly sure, what you would like to do, but you could just
> say, but maybe this answers your question:
>
> set sports; param favorite symbolic in sports;
>
> var train{sports} >=0;
>
> s.t. foobar: train[favorite] >=2;
>
> minimize work: sum{f in sports} train[f];
>
> data;
>
> set sports := running cycling swimming; param favorite := 'running';
>
> end;
>
>
> So put ' around the name for a symbolic parameter, and also don't put
> comma between set elements.
>
> I hope this helped. If not, please clarify your situation.
>
> All the best,
>
> Mate
>
>
>> set := A, B, C;
>>
>> param some_element_in_set, symbolic := ?????;
>>
>> The closest I saw was in this old help-glpk email:
>> https://lists.gnu.org/archive/html/help-glpk/2006-11/msg00059.html
>>
>> Which says:
>>
>> set S;
>>
>> param ref{i in 1..card(S)}, symbolic, in S;
>>
>> # ref[i] refers to i-th element of S;
>>
>> param a{S};
>>
>> ... a[ref[i]] ... # means a[i-th element of S]
>>
>> But I cannot get this to work. If I could get it to work, then I
>> would do something like: param some_element_in_set := ref[1];
>>
>> BTW, I’m still hoping that someone will help solve how to work the
>> sudoku_excel.mod example in the ‘examples\sql’ directory of the GLPK
>> directory under Windows 10 64bit. I still cannot get that to work.
>>
>> -Marc
>>
>