[Octave-bug-tracker] [bug #56798] semilogy - "omitting non-positive data in log plot" and empty plot with all positive data

[anonymous]

URL:
  <https://savannah.gnu.org/bugs/?56798>

                 Summary: semilogy - "omitting non-positive data in log plot"
and empty plot with all positive data
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Fri 23 Aug 2019 11:40:42 AM UTC
                Category: Plotting
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Unexpected Error
                  Status: None
             Assigned to: None
         Originator Name: Andrea Baldoni
        Originator Email: address@hidden
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 4.0.3
        Operating System: GNU/Linux

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Details:

I found a behavior I don't understand.

This code:
(please note the abs function; f come from fft,
abs(f) has values from 0 to ~0.53, minimum non-zero value
is about 1e-15 - of course no negative values)

semilogy(range, abs(f([range])));

produce a completely empty plot and this warning

warning: axis: omitting non-positive data in log plot
warning: called from
    __line__ at line 122 column 16
    line at line 56 column 8
    __plt__>__plt2vv__ at line 500 column 10
    __plt__>__plt2__ at line 246 column 14
    __plt__ at line 113 column 17
    semilogy at line 60 column 10
    myfile.m at line 75 column 1

but works if I modify it in:

semilogy(range, abs(f([range]))+10^-14);

(or 10^-30, or 10^-50, just changes the scale of plot).

plot() works perfectly without adding anything.

Where is the problem? It's really a bug in semilogy?

Andrea Baldoni




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