Comments on: Graph Structured Stacks in Clojure

By: cgrand

cgrand — Tue, 09 Mar 2010 19:19:22 +0000

@Chris, thanks for the link: it’s interesting to see the same structure applied ti different usecases. By the way GSS are not mine: it’s part of Tomita’s GLR algorithm http://en.wikipedia.org/wiki/GLR_parser.

By: Chris

Chris — Tue, 09 Mar 2010 18:35:54 +0000

You’ve rediscovered Boolean Decision Diagrams, which are used to represent combinatorial logic functions for circuit optimization and verification.

http://en.wikipedia.org/wiki/Binary_decision_diagram

By: links for 2010-01-19 « Blarney Fellow

links for 2010-01-19 « Blarney Fellow — Wed, 20 Jan 2010 01:41:59 +0000

[...] Clojure and me » Graph Structured Stacks in Clojure (tags: clojure graph) [...]

By: cgrand

cgrand — Tue, 19 Jan 2010 10:36:50 +0000

Sean, Eric,

Adjency lists are indeed nice for general graph processing but one doesn’t usually implement, for example, linked lists with adjency lists.
I’m exploring specialized representations for GSS. I’ll keep you posted as I progress: experiment will tell us if a specialized representation is worth its complexity.

By: Eric Normand

Eric Normand — Sun, 17 Jan 2010 23:06:06 +0000

Christophe,

I also like to keep my graphs as a set of edges. It matches the mathematical definition of a graph:

A set of vertices V and a set of edges E: {V, E}. The edge is a map like this {:a 7 :b 3} so that it’s directed. It’s also easy to add labels to the edges if you need them.

All sorts of graph operations are easier with this method. You could also build an index of this if you really needed fast lookup times. The index would be vertex to a set of edges containing that vertex. Or you could build two indexes, one for the :a position and one for the :b position.

see you later

Eric

By: Sean Devlin

Sean Devlin — Sat, 16 Jan 2010 17:28:55 +0000

Christophe,
I have to work with a lot of (directed) graphs on the clock. I have found it very useful to simply keep track of a edges. So, I would do something like this

[{:source 7 :dest 3}
{:source 7 :dest 4}
{:source 7 :dest 5}
{:source 3 :dest 1}
{:source 4 :dest 1}
{:source 8 :dest 6}
{:source 5 :dest 2}
{:source 6 :dest 2}
{:source 1 :dest 0}
{:source 2 :dest 0}]

This also makes it very simple to determine what are direct dependencies with a simple filter, and all dependencies with a simple recursive call. It also fits with a classic RDBMS well, or a NoSQL alternative.

HTH,
Sean