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Jesper,
Can you open an issue on this on github. If you are feeling ambitious a
pull request fixing the bug (as you seem to have a good idea of where the
problem is) would also be great!
Tom
On Fri, Apr 24, 2015 at 8:38 AM Jesper Larsen <jes...@gm...>
wrote:
> Hi Matplotlib Users,
>
> When I make wind barbs with rounding enabled and custom barb increments I
> noticed that there were no wind barbs with half barbs above 2 full barbs.
> The reason seems to be a bug in the _find_tails method. The bug is
> illustrated by this small script (_find_tails is a copy of the one in
> matplotlib):
>
> import numpy as np
>
> def _find_tails(self, mag, rounding=True, half=5, full=10, flag=50):
> '''
> Find how many of each of the tail pieces is necessary. Flag
> specifies the increment for a flag, barb for a full barb, and half for
> half a barb. Mag should be the magnitude of a vector (ie. >= 0).
>
> This returns a tuple of:
>
> (*number of flags*, *number of barbs*, *half_flag*, *empty_flag*)
>
> *half_flag* is a boolean whether half of a barb is needed,
> since there should only ever be one half on a given
> barb. *empty_flag* flag is an array of flags to easily tell if
> a barb is empty (too low to plot any barbs/flags.
> '''
>
> #If rounding, round to the nearest multiple of half, the smallest
> #increment
> if rounding:
> mag = half * (mag / half + 0.5).astype(np.int)
>
> num_flags = np.floor(mag / flag).astype(np.int)
> mag = np.mod(mag, flag)
>
> num_barb = np.floor(mag / full).astype(np.int)
> mag = np.mod(mag, full)
>
> half_flag = mag >= half
> empty_flag = ~(half_flag | (num_flags > 0) | (num_barb > 0))
>
> return num_flags, num_barb, half_flag, empty_flag
>
> def main():
> mag = np.arange(0,21,1)
> barb_incs = {'half': 2.57222,
> 'full': 5.14444,
> 'flag': 25.7222}
> print 'With rounding'
> num_flags, num_barb, half_flag, empty_flag = _find_tails(None, mag,
> rounding=True, **barb_incs)
> for i in range(len(mag)):
> print mag[i], num_flags[i], num_barb[i], half_flag[i],
> empty_flag[i]
> print 'Without rounding'
> num_flags, num_barb, half_flag, empty_flag = _find_tails(None, mag,
> rounding=False, **barb_incs)
> for i in range(len(mag)):
> print mag[i], num_flags[i], num_barb[i], half_flag[i],
> empty_flag[i]
>
> if __name__ == '__main__':
> exit(main())
>
> It seems like the error is not present when the barb increments are not
> set. I believe the reason for the bug is the float comparison (half_flag =
> mag >= half) where the value is rounded to a value very close to/identical
> to the 'half' increment. And it seems like python does the right thing when
> the "half" increment is a whole number but not always when it is not.
>
> But in any case the code should probably not depend two floats being equal.
>
> Best regards,
> Jesper
>
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