From: "M. Edward (Ed) Borasky" <znmeb@...>
Date: 2006-08-07T00:46:27+09:00
Subject: Re: Resubmitting legacy RCR 161

Dave Burt wrote:
> M. Edward (Ed) Borasky wrote:
>   
>> Some time back, RCR 161 was submitted to add a []= method to the Matrix
>> class defined in "matrix.rb". Apparently, this was imported from an
>> older database and needs to be resubmitted. Can "anyone" (for example,
>> me) do that, or does it have to be the original submitter?
>>     
>
> The problem with this RCR, if I recall correctly, is that Matrix objects
> are immutable, and []= is a mutation operation.
>
> There's room for methods that return a copy of the matrix modified in a
> given way, but you can't change self.
>
> Cheers,
> Dave
>   
I guess I need to define my own "Matrix" class then. Making a copy of a 
200x200 matrix to change one element, or in my case the whole upper 
triangle, is not going to work. I ended up doing "a = m.to_a", changing 
the upper triangle in "a", and then doing "m = Matrix.rows(a)". Until I 
looked at the code, I thought Matrix was either inheriting from or 
mixing in Array.

Still, at least one other person -- the person who filed RCR 161 -- 
thought that "m[i, j] = -1" was something a "Matrix" object like "m" 
should know how to do. It's such a common operation in matrix 
computations that its non-existence seems more like an oversight than a 
design feature or a bug to me. And it violates the principle of being 
able to write FORTRAN code in any language. :)