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Re: [Help-glpk] Ordered sets in GMPL
From: |
Nigel Galloway |
Subject: |
Re: [Help-glpk] Ordered sets in GMPL |
Date: |
Mon, 29 Dec 2008 16:26:19 +0100 |
I can't agree with either position here. The concept of well ordered sets is
fundamental to arithmatic. examples/t1.cs depends on the mathmatical proof that
any subset (however complex the derivation) of a well ordered set is a well
ordered set. There is a proof that the square root of two must be irrational by
showing that the well ordered set of rational solutions has no minimum value.
The set of orders with due date is not well ordered. In what sense is an order
for 10 tons of coal due on Jan 1st. 2009 less than or greater than an order for
5 tons of tomatoes due on Jan 1st. 2009?
Dates are a tricky subject. Note that there is no year zero in the revealed
calendar, unlike GLPK's implementation.
> ----- Original Message -----
> From: "glpk xypron" <address@hidden>
> To: "Andrew Makhorin" <address@hidden>
> Cc: address@hidden
> Subject: Re: [Help-glpk] Ordered sets in GMPL
> Date: Wed, 24 Dec 2008 22:39:01 +0100
>
>
> Hello Andrew
>
> > The point is that the set is not the same as array, and formally it is
> > an unordered collection. In which context do you need a set to be ordered?
>
> In as scheduling problem I have a set of orders with due date and
> release date.
> Objective is some weighted function of setup cost, tardiness and earliness.
>
> I want the result to be output in the sequence of the scheduled date.
>
> Best regards
>
> Xypron
>
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