[Help-glpk] [Fwd: Redundant Set Elements and Generation Time]

[Andrew Makhorin]

-------- Forwarded Message --------
From: Andrew B. Martin <address@hidden>
To: address@hidden
Subject: Redundant Set Elements and Generation Time
Date: Sat, 22 Jun 2013 16:04:57 -0300

Hello,

I have some inventory variables defined by the following constraint set:

inventory_1{x in X, y in Y, t in 0..20}:
INVENT_1[x,y,t] = sum{ (i,j) in set_1 : attribute_1[i] = x and 
attribute_2[i] = y } d[t]*x[i,j];

i, referenced above, can have attribute_1:= 0,1,2 in periods t = 0,1,2; 
but in all later periods, t>2, all i have attribute_1:= 0.

The set X:= {0,1,2} for the entire modelling horizon; the elements {1,2} 
are redundant after t>2.

Does this adversely affect model generation time?

I feel like it would be faster if X:={0,1,2} when t<=2 and X:={0} when 
t>2 but I can't think of anyway to do this other than make two sets of 
constraints:

e.g.,
inventory_1a{x in Xa , y in Y, t in 0..2 }:
INVENT_1a etc

and
inventory_1b{x in Xb, y in Y, t in 3..20}:
INVENT_1b etc

This would get messy in my model.

Can anyone think of any other approaches?

Regards,
Andrew