From: Mathieu Bouchard <matju@...>
Date: 2006-03-14T07:27:15+09:00
Subject: Re: how to introduce reference objects into ruby

On Tue, 14 Mar 2006, Geert Fannes wrote:

> and if it is choosen to be smaller to have a better fit, this becomes
> virtually the same as storing each element separately. But I could be
> wrong since I never tried this. Have you experience with this?

Ok, I haven't tried it, and doing it efficiently enough might mean using a
clustering algorithm that will pack similar columns and rows closer
together so that they take less space. If you don't do it, the method of
storing a pair of hashes of hashes is more efficient. There are questions 
of graph density that I haven't investigated (what's the expectancy of 
space taken by the data given a certain probability that a certain pair 
of vertices has an edge between them...).

BTW, if you make your matrix element assignment operator do two
assignments (one to the row-major representation and one to the
column-major representation), then you might not need references.

In Ruby, there's the []= and [] operators which you can define together.
The []= can play both the role of subscripting and assignment without
needing any intermediate references. Also, Ruby's subscript operator can 
take any number of arguments. The right-handed value is always the last in 
the list of args.

class MyMatrix
  ...
  def []=(i,j,value)
    @rows[i][j]=value
    @columns[i][j]=value
  end
end

mm=MyMatrix.new
mm[3,5] = 42

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| Freelance Digital Arts Engineer, Montr�al QC Canada