Re: [boost] wrong result in complex pow

1 Feb 2021

      Hello Chris,
your patch doesn't seem to be working properly yet. I also noticed that there is the same problem with NaN and inf (and zeros?) for pow(complex, complex). I'm currently working on tests for all pow functions and patches. Hope I'll get this ready soon and send it to you. 

thx
Gero

Am 01.02.21 um 14:41 schrieb Christopher Kormanyos:
...
...
...
 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 relevant
tests. Underway, I did find that more
possible work with zero, inf, NaN parameters
that *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 requests
for changes. I'd probably end up breaking
existing code if I tried to clean up all
kinds of edge cases that my eyes happened
across.
That being said, the exact issue that you
have pointed out and addressed in this
thread on the board is being handled
in the PR here:
https://github.com/boostorg/math/pull/507 https://github.com/boostorg/math/pull/507
... with fixed code here:
https://github.com/boostorg/math/blob/e3cc94a580f3d1282578b0c31f985a392c866f... https://github.com/boostorg/math/blob/e3cc94a580f3d1282578b0c31f985a392c866f...
Gero, if you get a chance, could you
give the patch a try? It will expectedly be
merged in and available in the next release.
Kind regards, Chris
On Sunday, January 31, 2021, 3:22:53 PM GMT+1, Christopher Kormanyos  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 Infinities
are correct yet,... But the patch is generally
moving toward the fix shown in the link below...
If you get a chance, could you try that patch
from the branch linked below?
https://github.com/boostorg/math/blob/2eac693e12547c1ca26800c2403e4e50f62d29... https://github.com/boostorg/math/blob/2eac693e12547c1ca26800c2403e4e50f62d29...
Kind regards, Chris
On Sunday, January 31, 2021, 2:17:32 PM GMT+1, Gero Peterhoff  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 https://godbolt.org/z/8Me15Y
regards
Gero
Am 30.01.21 um 16:22 schrieb Christopher Kormanyos:
...
...
...
 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 ><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 mailto:boost@lists.boost.org> wrote:
Hello,
the pow-function pow(scalar, complex) in boost/math/cstdfloat/cstdfloat_complex_std.hpp get wrong result.
Current implementation:
inline complex pow(const BOOST_CSTDFLOAT_EXTENDED_COMPLEX_FLOAT_TYPE& x,
                                                                const complex& a)
{
  return std::exp(a * std::log(x));
}
I think that's correct:
inline complex pow(const BOOST_CSTDFLOAT_EXTENDED_COMPLEX_FLOAT_TYPE& x,
                                                                const complex& a)
{
  return std::exp(a * std::log(complex(x)));
}
regards
Gero
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