[Python-ideas] [RFC] draft PEP: Dedicated infix operators for matrix multiplication and matrix power

[Robert Kern]

On 2014-03-15 12:06, Antoine Pitrou wrote:
> On Sun, 16 Mar 2014 00:55:09 +1300
> Greg Ewing <greg.ewing at canterbury.ac.nz> wrote:
>> Antoine Pitrou wrote:
>>
>>> The possible reason given in the PEP is very weak and amounts to
>>> premature optimization:
>>
>> I don't think it's just a matter of optimization. Often,
>> matrix @ vector represents a linear operator acting on an
>> element of a vector space. When you chain them,
>>
>>      A @ B @ C @ v
>>
>> conceptually represents acting on v with C, then B,
>> then A.
>
> It can just as well represent "acting" on v with (A @ B @ C).
>
> Of course, mathematically it shouldn't make a difference, but in
> computer programming right-associative operators are always a special
> case, and therefore an additional cognitive burden.

I think his point was that people doing linear algebra tend to read these 
expressions "right-to-left" anyways because of that conceptual model. I'm not 
entirely sure how supportable that is in the general population, but it's 
certainly the way I think about these expressions. For me, left-associative 
causes an additional cognitive burden, but it's a minor one, either way.

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
  that is made terrible by our own mad attempt to interpret it as though it had
  an underlying truth."
   -- Umberto Eco