Re: [Help-glpk] Ordered sets in GMPL

[Nigel Galloway]

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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