Re: Putting features in vs. leaving them out, especially functions
On Wed, May 25, 2011 13:35, John Pryce wrote:
> Arnold
> Thanks, that modifies my opinion. But what's the justification for
> including these particular ones? What about something like
> (log(1-x) - x)/x^2 or (atan(x) - x)/x^3 or ...?
> When you need THOSE, do you code them yourself?
The functions dividing the difference to a Taylor expansion by x and x^2
are needed for _every_ basic elementary function to get sharp first and
2nd order slopes.
Currently, we code them all ourselves, but this is slow. Using continued
fractions or lookup tables would be better, but we weren't patient enough
to do it.
> John
>
> On 25 May 2011, at 12:18, Arnold Neumaier wrote:
>> On Wed, May 25, 2011 10:06, John Pryce wrote:
>>> Stuff like (1-cos x)/x^2: people to whom these are important are
>>> competent enough to code them themselves; they are unlikely to be
>>> performance-critical.
>>
>> They are needed for the efficient implementations of slopes and
>> second-order slopes, which we use in our COCONUT global optization
>> environment almost as much as CP.
>
>