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
> <[email protected]> On Behalf Of
> Mate Hegyhati Sent: Thursday, December 12, 2019 2:29 AM To:
> [email protected] 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
>> 
>