From: Brock Lee <broclee@...>
Date: 2006-12-11T08:55:04+09:00
Subject: Re: Complete Newbie - Matrix Question

Based on the documentation at ruby-doc.org, I would think that the
following would work for versions 1.8.5 and later.  But my version of
Ruby, 1.8.4, does not seem to support it.  Here it is:

    a[i, j] = field

One potential solution would be to put your data into an Array
initially, and then convert it to a Matrix at the end.  Assuming a is
an Array, the following would work:

    m = Matrix.rows(a)

By the way, a bit further down you have a conditional:

    if i = 5

which should be:

    if i == 5

Brock Lee


Jay wrote:
> Hi Folks,
> This is probably quite easy, but I can't find a Matrix function or way
> to populate a specific element of a matrix with a given value? ie, I
> want to tell that element i,j of matrix.a should be 3
> My code below is a simple test to populate a 5 by 5 matrix from values
> in a CSV text file. The loops etc are messy, but it's just an example.
>
>
> require "mathn"
> i=1
> j=1
> a = Matrix.zero(5)
> File.open("TestData.txt").each do |record|
>     record.split(",").each do |field|
>     field.chomp!
>     if i<5 then
>       Matrix.a(i,j)=field                #      <-------------How do I
> do this line?
>     end
>     if i = 5 then
>       i = 1
>       j=j+1
>     end
>     i=i+1
>    end
> end
> puts a.to_s
> 
> Any Help/pointers would be great.
> TIA.
> Jay.