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Re: [Help-glpk] modeling variable "chains"

From: Michael Hennebry
Subject: Re: [Help-glpk] modeling variable "chains"
Date: Thu, 13 Aug 2009 17:00:30 -0500 (CDT)
User-agent: Alpine 1.00 (DEB 882 2007-12-20)

On Thu, 13 Aug 2009, Yaron Kretchmer wrote:

I've modeled the resources, and created an array of binary variables which
describe whether a certain resource exists in a certain X/Y location.
I'm having difficulties modeling the "paths". My difficulty is this:
- Each path maps to a pattern of resources (for instance R1->R2->R2->R1). I
can successfully describe the path contents (i.e. the fact that it contains
2 R1's, and 2 R2's), but how can I describe the order i.e. how do I capture
the fact the pattern has to contain adjacent resources (i.e. you don't want
a path to include disjoint resources that are spread around your chip, you
want resources that are in adjanct X/Y coordinates.

So my question:
*) How do I model the constraint that the resources mapping to a path need
to have consecutive X or Y coordinates?

This is a lot like finding a path in a sparse graph.
Try having binary variables for the arcs instead of the nodes.

Michael   address@hidden
"Pessimist: The glass is half empty.
Optimist:   The glass is half full.
Engineer:   The glass is twice as big as it needs to be."

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