def PROFILE_DOPPLER(sg0,GamD,sg):
    """
    # Doppler profile.
    # Input parameters:
    #   sg0: Unperturbed line position in cm-1 (Input).
    #   GamD: Doppler HWHM in cm-1 (Input)
    #   sg: Current WaveNumber of the Computation in cm-1 (Input).
    """
    return cSqrtLn2divSqrtPi*exp(-cLn2*((sg-sg0)/GamD)**2)/GamD