Re: wrong result in complex pow

From: Christopher Kormanyos (e_float_at_[hidden])
Date: 2021-01-30 15:22:25

 >>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 itis not clear which code example elicitsthe unexpected behavior.

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,
                                                                const complex<BOOST_CSTDFLOAT_EXTENDED_COMPLEX_FLOAT_TYPE>& a)
{
  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,
                                                                const complex<BOOST_CSTDFLOAT_EXTENDED_COMPLEX_FLOAT_TYPE>& a)
{
  return std::exp(a * std::log(complex<BOOST_CSTDFLOAT_EXTENDED_COMPLEX_FLOAT_TYPE>(x)));
}

regards
Gero

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