[Octave-bug-tracker] [bug #59709] ode event handler function is incorrect when direction variable is [-1, -1]

[Rik]

URL:
  <https://savannah.gnu.org/bugs/?59709>

                 Summary: ode event handler function is incorrect when
direction variable is [-1, -1]
                 Project: GNU Octave
            Submitted by: rik5
            Submitted on: Thu 17 Dec 2020 08:05:09 AM PST
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: Confirmed
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
                 Release: 6.1.0
         Discussion Lock: Any
        Operating System: Any

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Details:

This report originated as a Help topic on Discourse:
https://octave.discourse.group/t/incorrect-events-handling-by-ode45/539/6.

The necessary files to reproduce the bug are attached.  Download all of them
and then run solve_myode.m.

The issue is in ode_event_handler.m


    ## Check if one or more signs of the event has changed
    signum = (sign (evtold) != sign (evt));
    if (any (signum))         # One or more values have changed
      idx = find (signum);    # Get the index of the changed values

      if (any (dir(idx) == 0))
        ## Rising or falling (both are possible)
        ## Don't change anything, keep the index
      elseif (any (dir(idx) == sign (evt(idx))))
        ## Detected rising or falling, need a new index
        idx = find (dir == sign (evt));
      else
        ## Found a zero crossing but must not be notified
        idx = [];
      endif


If none of the direction indicators are 0 (accept rising or falling edge) then
the elseif is executed and Octave can get the wrong index.  This will happen
for direction indicators which are all positive ([1, 1, ...]) or all negative
([-1, -1, ...]) as in this example case.



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File Attachments:


-------------------------------------------------------
Date: Thu 17 Dec 2020 08:05:09 AM PST  Name: myode.m  Size: 47B   By: rik5

<http://savannah.gnu.org/bugs/download.php?file_id=50497>
-------------------------------------------------------
Date: Thu 17 Dec 2020 08:05:09 AM PST  Name: solve_myode.m  Size: 1KiB   By:
rik5

<http://savannah.gnu.org/bugs/download.php?file_id=50498>

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