From: Dave Baldwin <dave.baldwin@3dlabs.com>
Date: 2008-10-10T16:37:18+09:00
Subject: Re: Bug in Vector class?


On 9 Oct 2008, at 18:12, Thomas B. wrote:

> Dave Baldwin wrote:
>> The Vector class doesn't seem to have any idea that it is  
>> representing
>> a row or column vector and as the class stands now a vector * matrix
>> will always fail.
>
> Vector.elements([1,2,3])*Matrix.identity(1)
> #=> Matrix[[1], [2], [3]]
>
> Of course it's not much of a useful operation, but for me it's evident
> from it that a vector assumes itself to be a vertical matrix each time
> it is required to behave like a matrix.
>
> And now, what will be the result of the above operation if, as you  
> want,
> a vector would auto-transpose when sent * with a matrix? A row or a
> column matrix?  For me, this proves that your idea is inconsistent. It
> is not true that vector*matrix operation is never possible, so we
> shouldn't automagically make it possible even if it is not. It  
> wouldn't
> make debugging any easier.

OK, so you demonstrated a degenerate case that is not much use as you  
point out.  How would you do something more useful such as  
Vector[1,2,3]*Matrix.identity(3)?  I don't think you can unless you  
convert the vector to a row vector aka a matrix with one row and do it  
as a matrix * matrix operation.

Also a Vector * Matrix should return a Vector and not a Matrix (as the  
Matrix * Vector operation does).

Thankfully with open classes I can get the behaviour I think is  
desirable.

Dave.



>
>
> TPR.
> -- 
> Posted via http://www.ruby-forum.com/.
>