[Octave-bug-tracker] [bug #62094] log1p returns wrong result for complex input

[anonymous]

URL:
  <https://savannah.gnu.org/bugs/?62094>

                 Summary: log1p returns wrong result for complex input
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Mon 21 Feb 2022 09:28:10 PM UTC
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: Vincent
        Originator Email: vmagnoux20@gmail.com
             Open/Closed: Open
                 Release: 6.4.0
         Discussion Lock: Any
        Operating System: GNU/Linux

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Details:

When using a complex number as input, the log1p function seems to give the
wrong result. For example:


octave:37> log1p(0.1i)
ans =  4.9752e-03 + 1.4711e+00i


but the result should actually be something like 4.975e-3 + 9.97e-2i
(according to numpy).

This is more obvious on smaller inputs "x", where the output of log1p seems to
converge on 1.5708i rather than a value close to x.


octave:40> log1p(0.0001i)
ans =  5.0000e-09 + 1.5707e+00i


I have also seen this in version 4.2.2




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