From: Surendra Singhi <efuzzyone@...>
Date: 2006-09-13T03:28:21+09:00
Subject: Re: Matrix

Hi,
Paul Lutus <nospam@nosite.zzz> writes:

> MonkeeSage wrote:
>
> / ...
>
>> Anyhow, I don't really care if []= is there by default, I can add it if
>> I want it; but I just don't understand why "a matrix [as a value] is
>> immutable" means that []= shouldn't be there regarding the data
>> structure.
>
> You might as well ask why there is no formal method to change the third
> digit of an integer in class Fixnum. 

irb(main):001:0> x="hello"
=> "hello"
irb(main):002:0> x[0] = 'w'
=> "w"
irb(main):003:0> x
=> "wello"

Why is the above allowed? By the same argument, shouldn't strings be
immutable. 
>
> Most matrix operations operate on matrices as units. Here's an example, a
> matrix from my library, responsible for rotating objects in three-space:

I don't agree, the only example which I have heard is people talking about
matrix rotation, what about scaling matrices, there are several other matrix
operations. 

>    def convert_3d_to_2d(x,y,z,anaglyph_flag)
>       x = (x * (PerspectiveDepth + z))/PerspectiveDepth
>       x += z * anaglyph_flag * AnaglyphScale if anaglyph_flag
>       y = (y * (PerspectiveDepth + z))/PerspectiveDepth

Ruby should allow these operations in place, what if you want to scale just
one row? 

Is there any guarantee, the implementation of matrix won't change, and "@rows"
will be there forever?

Cheers,

-- 
Surendra Singhi
http://ssinghi.kreeti.com, http://www.kreeti.com
Read my blog at: http://cuttingtheredtape.blogspot.com/
,----
| Great wits are sure to madness near allied,
| And thin partitions do their bounds divide.
| 
|     (John Dryden, Absalom and Achitophel, 1681)
`----