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##### coordsys.frequencytofrequency - Function

1.1.3 Apply relativistic Doppler shift to a list of frequencies

Description

This function converts frequencies to frequencies by applying a relativistic Doppler shift: fout = fin * sqrt((1.-v/c)/(1.+v/c)) .

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).

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

Arguments

 Inputs value Frequencies to convert allowed: doubleArray Default: frequnit Unit of input frequencies. Default is unit of the spectral coordinate. allowed: string Default: velocity Velocity allowed: any Default: variant
Returns
doubleArray

Example

"""
ia.open(’M100line.image’)
mycs = ia.coordsys()
ia.close()

mycs.frequencytofrequency(value=[115271201800.0], frequnit=’Hz’, velocity=’1000km/s’)
results in
array([114887337607.0])

Let’s see if this is correct
print 115271201800.0*sqrt((1.-1000000./299792458.0)/(1.+1000000./299792458.0))
Result: 1.14887337607e+11
"""

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