[AstroPy] Tying model bounds to other parameters in compound models

[Azalee Bostroem]

Hi,

I am trying to fit the [OI] doublet at 6300, 6364 A as a compound model (Const1D+Gaussian1D+Gaussian1D). This doublet has a known ratio range of 1:1 to 1:3 and I would like fix the bounds of the amplitude of the second gaussian to be between 1/3 and 1 times the amplitude of the first gaussian. I know its possible to tie model parameters to each other (e.g. 
def fix_offset(oi_emission):
    mean_2 = oi_emission.mean_1 + 64
    return mean_2

emission_model.mean_2.tied = fix_offset
) and to set bounds on parameters (e.g.
emission_model.amplitude_1.min = 0
). Is it possible to tie bounds to other parameters? My naive approach of 

def fixed_amp_ratio(oi_emission):
    amplitude_2.min = 0.3*oi_emission.amplitude_1
    return amplitude2.min

emission_model.amplitude_2.min.tied = fixed_amp_ratio
 Didn’t work because min has no attribute tied.

Please let me know if I’ve missed anything,

Thanks,
Azalee
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