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PMVector/PMMatrix >> #dot: does not compute a dot product. #29
Description
Currently, #* computes the dot product:
#(1 2) asPMVector * #(2 1) asPMVector. "4"
and #dot: computes elementwise multiplication:
#(1 2) asPMVector dot: #(2 1) asPMVector. "a PMVector(2 2)"
#dot: should probably be renamed to something like #elementwiseMultiply: or maybe a shorter binary message.
Activity
olekscode commentedon May 18, 2017
I think I could swap them.
But wouldn't it silently break all the code that has ever used this multiplication?
emdonahue commentedon May 18, 2017
Yes, for that reason I think swap is a bad idea. Moreover, #* is a natural message for dot product because that is what we would expect, from the mathematical notation, to be polymorphic with scalars. Still, having #dot: not compute the dot product is probably not ideal under any circumstances. My thought would be to leave the default multiplication #* as the dot product, make #dot: just delegate to #*, and add a new method for elementwise multiplication.
SergeStinckwich commentedon May 18, 2017
We can try to swap because I don't silent breaks ;-) we have also a lot of tests to cover these kind of changes. Before that we can have a look to dot: implementors if they are any others.
emdonahue commentedon May 18, 2017
I don't think we should swap. I didn't fully think it through before I made that suggestion. Dot product IS the default multiplication for matrices and vectors, so it makes sense to leave #* as the dot product. I think all we need to do is rename #dot: to something like #elementwiseMultiply: or maybe some shorter binary message.
nicolas-cellier-aka-nice commentedon Aug 2, 2017
Indeed, dot: is misleading and should be renamed...
But I never saw
*used for dot product elsewhere. Usually it can be array product (element-wise), or matrix product (matrix*vector), or external product in a space vector (scalar*vector).If
*is both dot product and scalar product, then(u*v)*w ~= u*(v*w)hemalvarambhia commentedon Apr 24, 2019
I had a quick look at wikipedia and this binary operation is referred to as the Hadamard product (or Schur product/entrywise product) and the symbol used to refer to it is a circle with a dot inside it. Could we call the message
circleDotinstead ofdot?SergeStinckwich commentedon Apr 24, 2019
yes better to be more precise. Maybe
hadamardProduct?hemalvarambhia commentedon Apr 30, 2019
I think we can introduce
hadamardProductas you say and deprecate thedotmessage, after your mentioning your concern about silent breaks.