Re: [boost] Boost Digest, Vol 1227, Issue 2
G'day all. Quoting Paul A Bristow <pbristow@hetp.u-net.com>:
I have been exploring the use of Stephen Moshier's Cephes Library in C (which the author has agreed to make available under the Boost license) to provide an implmentation of many of these functions,
Excellent! I added the list of functions in TR1 to the wiki (SpecialFunctions). Could you (or someone) please go through the list and add anything that's already in Cephes? Then we can take a look at what's left.
AND the other missing, and in many cases MUCH more important IMHO, math 'special' functions, mainly requiring the Incomplete beta function, as I proposed
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2004/n1668.pdf
but which was rejected as 'too difficult' - for which I suspect means 'too expensive').
Certainly not "too expensive" in terms of computing resources; as I understand it, incomplete beta is no harder to compute than gamma. Perhaps they meant too difficult to get a useful TR out that people would actually be able to implement in reasonable time? Cheers, Andrew Bromage
Please see http://www.boost.org/more/discussion_policy.htm#effective ajb@spamcop.net writes:
G'day all.
Quoting Paul A Bristow <pbristow@hetp.u-net.com>:
I have been exploring the use of Stephen Moshier's Cephes Library in C (which the author has agreed to make available under the Boost license) to provide an implmentation of many of these functions,
Excellent!
I added the list of functions in TR1 to the wiki (SpecialFunctions). Could you (or someone) please go through the list and add anything that's already in Cephes? Then we can take a look at what's left. ...
-- Dave Abrahams Boost Consulting www.boost-consulting.com
| -----Original Message----- | From: boost-bounces@lists.boost.org | [mailto:boost-bounces@lists.boost.org] On Behalf Of ajb@spamcop.net | Sent: 27 September 2005 03:20 | To: boost@lists.boost.org | Subject: Re: [boost] Boost Digest, Vol 1227, Issue 2 | AND the other missing, and in many cases MUCH more | important IMHO, math 'special' functions, | > mainly requiring the Incomplete beta function, | > as I proposed | > | > http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2004/n1668.pdf | > | > but which was rejected as 'too difficult' - for which I | suspect means 'too expensive'). | | Certainly not "too expensive" in terms of computing resources; as I | understand it, incomplete beta is no harder to compute than gamma. | Perhaps they meant too difficult to get a useful TR out that people | would actually be able to implement in reasonable time? The expense is the brain power required to produce a high quality implementation which proved more than expected for TR1 functions. IMO part of the problem is the unrealistic expectation of the Standards WGs for an accuracy similar to that for most of the other functions like sin, cos for which it IS feasible, albeit with care and skill, to get within a bit (ulp) or few. For some of the other functions, getting within a few decimal places is challenging. But the results are still far more accurate than required to be 'fit for purpose' in real-life statistics applications, like comparing two means to assess the probablity that they are different. Paul Paul A Bristow Prizet Farmhouse, Kendal, Cumbria UK LA8 8AB +44 1539 561830 +44 7714 330204 mailto: pbristow@hetp.u-net.com www.hetp.u-net.com
"Paul A Bristow" <pbristow@hetp.u-net.com> writes:
The expense is the brain power required to produce a high quality implementation which proved more than expected for TR1 functions.
IMO part of the problem is the unrealistic expectation of the Standards WGs for an accuracy similar to that for most of the other functions like sin, cos for which it IS feasible, albeit with care and skill, to get within a bit (ulp) or few.
For some of the other functions, getting within a few decimal places is challenging.
What leads you to believe there is such an unrealistic expectation? I don't see any mention of accuracy in the proposed TR (http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf for reference). -- Dave Abrahams Boost Consulting www.boost-consulting.com
David Abrahams <dave@boost-consulting.com> writes:
"Paul A Bristow" <pbristow@hetp.u-net.com> writes:
The expense is the brain power required to produce a high quality implementation which proved more than expected for TR1 functions.
IMO part of the problem is the unrealistic expectation of the Standards WGs for an accuracy similar to that for most of the other functions like sin, cos for which it IS feasible, albeit with care and skill, to get within a bit (ulp) or few.
For some of the other functions, getting within a few decimal places is challenging.
What leads you to believe there is such an unrealistic expectation? I don't see any mention of accuracy in the proposed TR (http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf for reference).
Never mind; obviously I should read entire postings before replying to them. Sorry :( -- Dave Abrahams Boost Consulting www.boost-consulting.com
participants (15)
-
ajb＠spamcop.net -
David Abrahams -
Paul A Bristow