Re: [boost] [math] asinh_test failing

From: Lars Gullik Bjønnes (larsbj_at_[hidden])
Date: 2006-09-24 16:50:16

"John Maddock" <john_at_[hidden]> writes:

| "Lars Gullik Bjønnes" wrote:
| > On gcc 4.1.1 glibc 2.4 x86_64 linux.
| >
| > If I use asinhf from glibc then the test works, if I use asinh from
| > boost::math then it fails. (This is for float)
| 
| Perplexing, it probably needs someone with an interest in numerics to debug 
| it on that platform to figure this out, especially as the asinh code for 
| that test case is a completely trivial:
| 
| return( log( x + sqrt(x*x+one) ) );
| 
| We might be able to eliminate a couple of obvious ones though: can you find 
| out what std::sinh(3.8F) returns?  First 9 digits please :-)

std::sinh(3.8F) =  22.3394069672
sinhf(3.8F)     =  22.3394069672 (*)

But perhaps more interesting:

asinhf(*)             = 3.79999995232
boost::math:asinhf(*) = 3.80000019073

And:
x = std::sinh(3.8F);

logf( x + sqrtf(x*x+one)         = 3.80000019073
log( x + sqrt(x*x+one)           = 3.79999995232
std::log( x + std::sqrt(x*x+one) = 3.80000019073

So it seems that glibc asinhf is using double precision internally,
and that this somehow contributes to makeing the testcase fail.

I think this is close to as far as I can test... far away from my
domain already.

| Then what happens if you add a boost::math:: qualifier to the asinh call in 
| asinh_test.hpp  and re-run the test?

In my tests that does not make a difference.
 
| I'm also pleased to see I'm not the only person who mis-types "math" as 
| "match"!! :-)

Hmm... must be the brain-stem in the fingers taking over.

-- 
	Lgb