[bug #57715] Discontinuity time - event missed - oops?

URL:
  <https://savannah.gnu.org/bugs/?57715>

                 Summary: Discontinuity time - event missed - oops?
                 Project: MCSim simulation sofware
            Submitted by: None
            Submitted on: Fri 31 Jan 2020 09:03:06 PM UTC
                Category: Sim
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: None
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any

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Details:

Frédéric,

This concerns modelu.c, line 286. A model that we're working on, and that
makes use of events, produces the diagnostic:

UpdateSpikes: Discontinuity was passed over...

I upgraded the diagnostic output to be more informative:

UpdateSpikes: Discontinuity was passed over:
sim time = 1.90000000000000010
event time = 1.89999999999999990

So, the issue of an event being passed over seems to be caused by comparing
two double precision numbers for equality, a perennial source of software
bugs. Your "Oops" comment in the source code suggests you thought this was an
accident waiting to happen.

I have not tried our model on Linux. We are building MCSim on Windows using
mingw. The cc switches are just -O3, and we're linking with GSL.

C99 gives us nextafter() and nextforward(). Using nextafter() seems to offer a
fix. See attached, lines 293-308. This corrects the issue for our model but I
think a more robust solution is required here.

Alex






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File Attachments:


-------------------------------------------------------
Date: Fri 31 Jan 2020 09:03:06 PM UTC  Name: modelu.c  Size: 24KiB   By: None

<http://savannah.gnu.org/bugs/download.php?file_id=48318>

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