initial loglikelihhod

[Atefeh Fakourrad]

Dear Prof. Bierlaire,

I am estimating a logit model using PandasBioegeme. The problem is that when I run the model, the initial loglikelihood significantly changes. For instance, I just move an attribute to another alternative and there is a huge difference in initial loglikelihood. Even if I do not change anything and just run the model for the second time, the initial loglikelihood gets equal to the final loglikelihood and this affects Rho-square. Apparently, the initial likelihood is relative to the previous model while I need an absolute initial loglikelihood. Is there any way to have the absolute initial likelihood? 

Best regards,

Ati. 

[Bierlaire Michel]

The initial likelihood is the likelihood for the initial values of the parameters. 

If you run several times Biogeme in the same directory, it saves previous estimates, and starts again from there, in order to save time. 

Two possibilities: 

- calculate the “null log likelihood”:  

biogeme.calculateNullLoglikelihood(av)

where av is the dictionary with the availability conditions.

It only depends on the data and the choice set.

- Disable the automatic saving of the parameters: 

biogeme.saveIterations = False

See documentation here:

http://biogeme.epfl.ch/sphinx/biogeme.html#biogeme.biogeme.BIOGEME.saveIterations

Make sure also to remove any file that looks like __mymodel.iter in the working directory.

Best regards,

Ati. 

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