Hi,
> A couple of months a go we already discussed the introduction of :
> reduce_rows<op_add>(A) vs reduce<op_add>(row_wise(A))
>
> And concluded that the latter option would lead to higher compilation
> times for not so much benefits.
>
> However, the more I think about it, the more I believe that reductions
> should be just internal tools and that we should provide direct
> shortcuts instead:
>
> sum(x), max(x), min(x), argmax(x), argmin(x)
>
> In this case, it would make much more sense to have
>
> sum(row_wise(A)), max(row_wise(A)), etc...
I like this :-) Which operations do we want to support? I think we
should cover the ones in MPI and OpenMP, i.e.
min(), max(), sum(), and prod(),
where the latter computes the product of all entries. For integers
there's also (L/B)AND, (L/B)OR, (L/B)XOR, with L referring to 'logical'
and 'B' to bitwise. OpenMP seems to allow a reduction with operator '-'
as well, which is somewhat exotic. What about summing absolute values
like in norm_1? What about summing squares as in norm_2()? It would be
nice to have them covered so that we don't need separate implementations
for the norms.
> rather than
>
> sum_rows, max_rows, etc...
>
> So I think that it could actually make sense to introduce
> {row|col}_wise(). Any thought?
How should row_wise(A) look implementation-wise? We can't make it a
vector_base, because of the padding of A (there is no range-object which
hides the zeros). This leaves us with matrix_expression, which is
probably okay (yet not a beauty), as it allows for easier overloading of
sum(), max(), etc.
Best regards,
Karli
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