Re: [eigen] sse asin implementation

[Benoit Jacob <jacob.benoit.1@xxxxxxxxx>]

2009/3/31 Rohit Garg <rpg.314@xxxxxxxxx>:
> On Tue, Mar 31, 2009 at 8:18 PM, Benoit Jacob <jacob.benoit.1@xxxxxxxxx> wrote:
>> What is the motivation for vectorizing asin in Eigen? Do you mean for
>> people who want a "cwise asin" on a vector? Do you have a use case for
>> this?
> Yes. The page on TODO says that transendental functions could be
> vectorized and since recently sin, cos, log, exp for floats were
> committed, I thought that eigen could do with other transcendental
> functions as well. I was planning to implement more transcendentals in
> the future, but if this is not useful, please tell me.

Well, the TODO only mentioned very common functions like sin, cos,
log, exp, for which use cases abound, for example, not long ago on
this list, Jos Vandenoever had a use case for vectorized cwise sin or
cos on vectors.

So vectorizing sin, cos, log, exp, as well as sqrt and perhaps
inverse_sqrt, is definitely useful.

But the inverse trigonometric functions like asin, acos, atan, are
much less commonly used. What's more, they tend to be used most of the
time on single isolated numbers, not on all coeffs of a vector. So
it's not clear if a vectorized asin would be used. I would prefer to
wait for use cases to appear.

I guess I should have replied sooner but since I didn't take part in
the earlier discussion I was hesitant.

Cheers,
Benoit