def MergeWaveSets(waveset1, waveset2):
"""Return the union of the two wavelength sets.
The union is computed using `numpy.union1d`, unless one or
both of them is `None`.
The merged result may sometimes contain numbers which are nearly
equal but differ at levels as small as 1E-14. Having values this
close together can cause problems due to effectively duplicate
wavelength values. Therefore, wavelength values having differences
smaller than or equal to ``pysynphot.spectrum.MERGETHRESH``
(defaults to 1E-12) are considered as the same.
Parameters
----------
waveset1, waveset2 : array_like or `None`
Wavelength sets to combine.
Returns
-------
MergedWaveSet : array_like or `None`
Merged wavelength set. It is `None` if both inputs are such.
"""
if waveset1 is None and waveset2 is not None:
MergedWaveSet = waveset2
elif waveset2 is None and waveset1 is not None:
MergedWaveSet = waveset1
elif waveset1 is None and waveset2 is None:
MergedWaveSet = None
else:
MergedWaveSet = N.union1d(waveset1, waveset2)
# The merged wave sets may sometimes contain numbers which are nearly
# equal but differ at levels as small as 1e-14. Having values this
# close together can cause problems down the line so here we test
# whether any such small differences are present, with a small
# difference defined as less than MERGETHRESH.
#
# If small differences are present we make a copy of the union'ed array
# with the lower of the close together pairs removed.
delta = MergedWaveSet[1:] - MergedWaveSet[:-1]
if not (delta > MERGETHRESH).all():
newlen = len(delta[delta > MERGETHRESH]) + 1
newmerged = N.zeros(newlen, dtype=MergedWaveSet.dtype)
newmerged[:-1] = MergedWaveSet[:-1][delta > MERGETHRESH]
newmerged[-1] = MergedWaveSet[-1]
MergedWaveSet = newmerged
return MergedWaveSet
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