Re: [Matplotlib-users] Unexpected beaviour when plotting narrow "peaks"

[Michael D. <md...@st...>]

It looks like the path simplification code is failing on this.  As a 
workaround, you can turn it off:

  rcParams['path.simplify'] = False

or reduce the threshold below which vertices are removed:

  rcParams['path.simplify_threshold'] = 0.0001

In the meantime, I'll look further into why this is failing.  Perhaps we 
need a lower default threshold.

Mike

Henrik Wallin wrote:
> Hello all,
>
> I'm sorry if this has been treated before, but I haven't found
> anything when searching the archives or the net.
>
> Basically, the problem surfaces when plotting FFT spectras using many
> data points. The amplitudes of the peaks in the spectra then seem to
> depend on the size of the plot window.
>
> Example code:
>
>
>   
>>>> from pylab import *
>>>> t=arange(65536)
>>>> plot(abs(fft(sin(2*pi*.01*t)*blackman(len(t)))))
>>>>         
> [<matplotlib.lines.Line2D object at 0x03871990>]
>   
>>>> show()
>>>>         
>
> With the original window size (WXAgg backend), I get maximum peaks at
> about 390. Zooming in on the peak will increase the amplitude.
> Resizing the window can also make the amplitude increase.
>
> The expected amplitude is:
>
>   
>>>> max(abs(fft(sin(2*pi*.01*t)*blackman(len(t)))))
>>>>         
> 12891.96683092583
>
> Is this a known problem, or should I file a bug report? Is there any
> workaround (except decreasing the length of t, and thus the level of
> detail)?
>
> I'm using ActivePython 2.6.3.7 for windows, matplotlib 0.99.1 binary,
> numpy 1.3.0 and wxPython-unicode-2.8.10.1. I've also tried with the
> TkAgg backend, which gives similar results.
>
> Thanks,
> Henrik
>
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-- 
Michael Droettboom
Science Software Branch
Operations and Engineering Division
Space Telescope Science Institute
Operated by AURA for NASA