Re: wrong result in complex pow

From: Gero Peterhoff (g.peterhoff_at_[hidden])
Date: 2021-01-31 13:17:29

Hello Christopher,
I just noticed that my simple patch with base=0 doesn't work. It is probably not that simple.
https://godbolt.org/z/8Me15Y

regards
Gero

Am 30.01.21 um 16:22 schrieb Christopher Kormanyos:
>>>Â the pow-function pow(scalar, complex) in
>>> boost/math/cstdfloat/cstdfloat_complex_std.hpp
>>> get wrong result.
> 
>> Thanks Gero,
>> I am on the go, but later today, I'll add this
>> as an issue in Git and kick off the discussion
>> for the fix with the colleagues.
> 
> A new issue can be found here, but it
> is not clear which code example elicits
> the unexpected behavior.
> 
> https://github.com/boostorg/math/issues/506 <https://github.com/boostorg/math/issues/506>
> 
> 
> On Thursday, January 28, 2021, 12:55:59 PM GMT+1, Gero Peterhoff via Boost <boost_at_[hidden]> wrote:
> 
> 
> Hello,
> the pow-function pow(scalar, complex) in boost/math/cstdfloat/cstdfloat_complex_std.hpp get wrong result.
> 
> Current implementation:
> inline complex<BOOST_CSTDFLOAT_EXTENDED_COMPLEX_FLOAT_TYPE> pow(const BOOST_CSTDFLOAT_EXTENDED_COMPLEX_FLOAT_TYPE& x,
> Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  const complex<BOOST_CSTDFLOAT_EXTENDED_COMPLEX_FLOAT_TYPE>& a)
> {
> Â  return std::exp(a * std::log(x));
> }
> 
> I think that's correct:
> inline complex<BOOST_CSTDFLOAT_EXTENDED_COMPLEX_FLOAT_TYPE> pow(const BOOST_CSTDFLOAT_EXTENDED_COMPLEX_FLOAT_TYPE& x,
> Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  Â  const complex<BOOST_CSTDFLOAT_EXTENDED_COMPLEX_FLOAT_TYPE>& a)
> {
> Â  return std::exp(a * std::log(complex<BOOST_CSTDFLOAT_EXTENDED_COMPLEX_FLOAT_TYPE>(x)));
> }
> 
> regards
> Gero
> 
> 
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