[Octave-bug-tracker] [bug #55354] incorrect result on complex step approximation example by prof. Higham

[anonymous]

URL:
  <https://savannah.gnu.org/bugs/?55354>

                 Summary: incorrect result on complex step approximation
example by prof. Higham
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Tue 01 Jan 2019 06:39:40 PM UTC
                Category: None
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: Alessandro Gentilini
        Originator Email: address@hidden
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 4.0.3
        Operating System: GNU/Linux

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Details:

I tried the example described at this page (see also attached files)

https://sinews.siam.org/Details-Page/differentiation-without-a-difference

and I get this result


f = (sym)

  atan(x)
  ────────
         2
       -x
  1 + ℯ

fd =  0.274623728154858
fd_cs =    1.09025432019950e+83
fd_fd1 =  0.250000000000000
fd_fd2 =  0.274623729288578


fd_cs is not as expected, it should be close to fd.



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File Attachments:


-------------------------------------------------------
Date: Tue 01 Jan 2019 06:39:40 PM UTC  Name: complex_step_example.m  Size:
438B   By: None

<http://savannah.gnu.org/bugs/download.php?file_id=45828>
-------------------------------------------------------
Date: Tue 01 Jan 2019 06:39:40 PM UTC  Name: complex_step.m  Size: 290B   By:
None

<http://savannah.gnu.org/bugs/download.php?file_id=45829>

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