Re: [Help-glpk] Modelling differences in time

[xypron]

Hello Jiri

Jiri K wrote:
> 
> Dear all,
> In my model I need to care about the values of a variable in consecutive
> periods. Therefore in the formulas I operate with differences like 
> 
> {i in PERIOD: i>1} x[i]-x[i-1]
> 
> However this only works when periods are described with numbers which
> always increment by 1. How could I simply model this if the members of the
> PERIOD set are e.g. 'Jan', 'Feb' etc?
> 

you will need a parameter translating the strings to numbers.

set PERIOD;
param month{p in PERIOD};
data;
set PERIOD := 
  Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec;

param month :=
  Jan 1 Feb 2 Mar 3 Apr 4 May 5 Jun 6 Jul 7 Aug 8 Sep 9 Oct 10 Nov 11 Dec
12;
end;

Best regards

Xypron

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