Re: [Help-glpk] New set functions

[glpk xypron]

Hello Nilo,

there is no expression in GMPL, which will return a single
element of a symbolic set. For a numeric set there is a
solution:

set A := {1..4};
param x{A};

solve;

printf "%s\n", 
  (if card({a in A : x[a] = 1}) = 0 then '*' else
  min{a in A: x[a] == 1} a );

data;

param x :=
  1  0
  2  1
  3  0
  4  1;
end;

Best regards

Xypron

-------- Original-Nachricht --------
> Datum: Wed, 2 Nov 2011 19:34:33 -0200
> Von: Nilo Cesar Teixeira <address@hidden>
> An: address@hidden
> Betreff: [Help-glpk] New set functions

> Hi all,
> 
> In my previous question (regarding printf and if), I thought about this
> expression which is invalid in current version of MathProg:
> 
> printf "%30s", (if card({name in I : H[name] = 1}) = 0 then '*' else
> XXXX);
> 
> My point is, I would like XXXX to be an expression which returns ONE
> element of a set. In this case, the value of 'name' for which H[name] = 1.
> *
> *
> I thought about these 2 functions which could be useful:
> 
>    1. first({name in I : H[name] = 1}), would return value of name; last()
>    would be good too;
>    2. member {name in I : H[name] = 1} (i), would return the ith member of
>    set.
> 
> So, member {name in I : H[name] = 1} (1) would return value of name too;
> 
> To really be effective, this should work with unsubscripted sets to, like
> set I := A NO THER MEM BER;
> 
> Suppose H[A] = 1, so the above functions return A.
> 
> What do you think ? Thank you.
> 
> -- 
> *Nilo Cesar Teixeira*
> address@hidden

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