1.1.3.0 coordsys.frequencytofrequency

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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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