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](http://np.int))
num_flags = np.floor(mag / flag).astype([np.int](http://np.int))
mag = np.mod(mag, flag)
num_barb = np.floor(mag / full).astype([np.int](http://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