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

**From**: |
Andrew Makhorin |

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

**Date**: |
Sat, 22 Jun 2013 23:34:36 +0400 |

-------- 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

**[Help-glpk] [Fwd: Redundant Set Elements and Generation Time]**,
*Andrew Makhorin* **<=**