Re: wrong result in complex pow

From: Christopher Kormanyos (e_float_at_[hidden])
Date: 2021-02-01 13:41:28

  >>Â noticed that my simple patch with base=0>> doesn't work.
> Thanks Gero.
> Yes. I am trying a patch that handles zero explicitly.> I'm not quite sure if all zeros, NaNs and Infinities> are correct yet,
Gero,
I patched this about as far as I'd like to go
for this particular issue, added relevanttests. Underway, I did find that morepossible work with zero, inf, NaN parametersthat *could* be done in that particular header,but I will not modify these at the moment.This is because there are not a lot of requestsfor changes. I'd probably end up breakingexisting code if I tried to clean up allkinds of edge cases that my eyes happenedacross.
That being said, the exact issue that youhave pointed out and addressed in thisthread on the board is being handledin the PR here:
https://github.com/boostorg/math/pull/507
... with fixed code here:https://github.com/boostorg/math/blob/e3cc94a580f3d1282578b0c31f985a392c866f19/include/boost/math/cstdfloat/cstdfloat_complex_std.hpp#L509
Gero, if you get a chance, could yougive the patch a try? It will expectedly bemerged in and available in the next release.
Kind regards, Chris
    On Sunday, January 31, 2021, 3:22:53 PM GMT+1, Christopher Kormanyos <e_float_at_[hidden]> wrote:  
 
  > noticed that my simple patch with base=0> doesn't work.
Thanks Gero.

Yes. I am trying a patch that handles zero explicitly.I'm not quite sure if all zeros, NaNs and Infinitiesare correct yet,... But the patch is generallymoving toward the fix shown in the link below...
If you get a chance, could you try that patchfrom the branch linked below?

https://github.com/boostorg/math/blob/2eac693e12547c1ca26800c2403e4e50f62d29bd/include/boost/math/cstdfloat/cstdfloat_complex_std.hpp#L512

Kind regards, Chris

    On Sunday, January 31, 2021, 2:17:32 PM GMT+1, Gero Peterhoff <g.peterhoff_at_[hidden]> wrote:  
 
 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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