[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
## Re: [Help-glpk] pick element from set?

**From**: |
glpk xypron |

**Subject**: |
Re: [Help-glpk] pick element from set? |

**Date**: |
Mon, 02 Jul 2012 07:42:56 +0200 |

Hello Kevin,
there is no function that will return an element of a set (except for
one-dimensional numeric sets).
You can create subsets.
e.g.
set X, dimen 2 := {(5, 7), (1, 10), (23, -3), ("y", "x"), ("a", "abc")};
set S := setof{(i,j) in X : forall{(k,l) in X} i <=k && j <= l} (i,j);
see
http://en.wikibooks.org/wiki/GLPK/GMPL_Workarounds#Sorted_output
Best regards
Xypron
-------- Original-Nachricht --------
>* Datum: Sun, 01 Jul 2012 03:11:00 -0400*
>* Betreff: [Help-glpk] pick element from set?*
>* Hello GLPK List,*
>* *
>* Is there a method to pick an arbitrary single item from a set? I don't *
>* care which one, but I need to have a single element from a set such that *
>* I can uniquely and consistently identify it.*
>* *
>* There is no order to the set, but /if/ there were an ordering to this *
>* set, I might reference this element as "nought". Put differently, say I *
>* have a set X:*
>* *
>* set X, dimen 2 := {(5, 7), (1, 10), (23, -3), ("y", "x"), ("a", "abc")};*
>* *
>* Is there functionality -- say a function called "pick()" -- to pick an *
>* arbitrary element from that set?*
>* *
>* Put another way, /if/ I could put that set into a list:*
>* *
>* list(X) == [(5, 7), (1, 10), (23, -3), ("y", "x"), ("a", "abc")]*
>* *
>* then I could get an arbitrary element, perhaps like 'get(list(X), 0)'.*
>* *
>* Is there a method to grab a single element from the set?*
>* *
>* I'll point out that I have an ad-hoc method of this for a *
>* single-dimensional set (using a nested setof structure and a comparison *
>* operator), but can't do it for any higher-dimensionality sets.*
>* *
>* Thanks,*
>* *
>* Kevin*
>* *
>* _______________________________________________*
>* Help-glpk mailing list*
>* address@hidden*
>* https://lists.gnu.org/mailman/listinfo/help-glpk*