Hey !
One thing I really like in Matlab is the operator.* , but well it doesn't
exist in general purpose languages :P
I think that operator* is mostly convenient for nested expressions.
However, since nested expressions often introduce temporaries that are
particularly expensive, I think that defining operator* may lead to bad
performance, leading some user to not realize that they are creating a lot
temporaries when they write i.e. A = B*C*D*E , while A = prod(B,
prod(C,prod(D,E))) is much more explicit in this regard. However, chosing
elementwise product for operator* would be super misleading in the case of
the matrix product (if someone writes A = B*C and ends up with some
elementwise product, he will be wtf'ed !).
Basically, i would personally leave all operator*(matrix,matrix),
operator*(matrix,vector) and operator*(vector,vector) undefined, but it's
just my personal opinion :) i'm not experienced with python and it might be
a great disappointment for the userbase if our syntax is too verbose (if
they are writing in python, they probably care a lot about verbosity!)
Best regards,
Philippe
2013/8/3 Toby St Clere Smithe <m...@tsmithe.net>
> Hi all,
>
> Suppose we have vectors v1 and v2. Then, we have four options for the
> semantics of "v1 * v2":
>
> 1) Element-wise product
> 2) Dot product
> 3) Outer product
> 4) Leave undefined
>
> Most of the time, in the rest of PyViennaCL, I've chosen semantics for
> the * operator that make sense given the context. For instance, for
> matrices m1 and m2, "m1 * m2" is the matrix product (not element-wise).
>
> So, I don't want to choose option (1), even though NumPy does this in
> places. NumPy is actually quite inconsistent: its "array" type is
> elementwise for all operators (*, /, +, etc; providing matrix product
> semantics for the "dot" method), but its "matrix" type has various
> semantics -- / is elementwise, but * is not, being the matrix product.
>
> This leaves (2) to (4). It seems ViennaCL itself leaves the * operator
> undefined, leaving the user to be explicit. I think I'm leaning towards
> this choice, for consistency, and to minimise confusion. But then why
> should I define the * operator for /any/ type? I think the answer is
> that, when someone has m1 and m2, "m1 * m2" is an operation they will
> want to be convenient -- more so than elementwise multiplication, or
> either the inner or outer product of vectors.
>
> But I'm not sure, hence this post.
>
>
> Best,
>
> Toby
>
>
>
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