1.1.3.0 coordsys.frequencytofrequency

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coordsys.frequencytofrequency - Function

1.1.3 Convert frequency to frequency with an offset
Description

This function converts frequencies to frequencies by applying (subtracting) a velocity offset.

The input frequencies are specified via a vector of numeric values and a specified unit (frequnit). If you don’t give a frequency unit, it is assumed that the units are those given by function coordsys units() for the spectral coordinate.

This function does not make any frame conversions (e.g. LSR to BARY) but you can specifiy the velocity doppler definition for the velocity via the doppler argument (see image summary() for possible values).

This function fails if there is no spectral coordinate in the Coordinate System. See also function frequencytovelocity.

This function presently uses an approximation only valid for velocities less than the speed of light. The correction tends to zero as the velocity appraches the speed of light. You will get NaNs for larger values of the velocity.

Arguments


Inputs
value	Frequency to convert
	allowed:	doubleArray
	Default:
frequnit	Unit of input frequencies. Default is unit of the spectral coordinate.
	allowed:	string
	Default:
velocity	Velocity offset
	allowed:	any
	Default:	variant
doppler	Velocity doppler definition
	allowed:	string
	Default:	radio

Returns
doubleArray

Example

"""
#
print "\t----\t frequencytofrequency Ex 1 \t----"
csys = cs.newcoordsys(spectral=T)
idx = [1.1,1.2,1.3,1.4,1.5]
rval = csys.referencevalue()
rv=rval[’numeric’][0]
freq=[]
for i in range(len(idx)):
freq.append(rv*idx[i])
print "In = [%.4e %.4e %.4e %.4e %.4e]" % tuple(freq)
#In = [1.5565e+09 1.6980e+09 1.8395e+09 1.9810e+09 2.1225e+09]
print cs.frequencytofrequency(freq, velocity=’100km/s’)
#[1555980894.0489383, 1697433702.5988414, 1838886511.1487448,
# 1980339319.698648, 2121792128.2485518]
#
"""

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