RE: next question - find some element of a set

[Meketon, Marc]

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
>