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Re: Plotting Problem

From: Dmitri A. Sergatskov
Subject: Re: Plotting Problem
Date: Sat, 26 Aug 2017 21:01:18 -0500

On Sat, Aug 26, 2017 at 7:35 PM, Dmitri A. Sergatskov <address@hidden> wrote:
On Sat, Aug 26, 2017 at 6:43 PM, Thomas D. Dean <address@hidden> wrote:

octave:27> loglog(f,Pxx);
warning: axis: omitting non-positive data in log plot
warning: called from
    __line__ at line 120 column 16
    line at line 56 column 8
    __plt__>__plt2vv__ at line 502 column 10
    __plt__>__plt2__ at line 248 column 14
    __plt__ at line 113 column 17
    loglog at line 60 column 10

​This warning is benign -- it's a long-stanging buglet in signal package (which I thought
was fixed some time ago, but apparently reappears again):
the spectral power ​must be positive, but due to finite numerical precision one could get
it negative.

​So I was wrong -- the problem is that f starts at 0 and you cannot plot that in loglog ​plot.
The loglog() function is trying to do something clever about it, but that messes up some
plot properties.
You can get rid of this problem for now by setting f(1) to some small value (<< f(2)).


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