Biogeme 3.2.14 - piecewise_variables raises when expression is not of type Variable

[Luca Bataillard]

Hello everyone,

I was completing this notebook from the Selected topics on Discrete Choice MOOC and ran into an issue with the models.piecewise_variables function crashing. Since the TRAIN_COST_SCALED variable is a composite Expression (runtime type of Division), it is not of type Variable and fails the check on line 75 of models/piecewise.py and raises an exception.

However, this notebook worked and produced correct results in version 3.2.13, and also works if we change the line in 3.2.14's models/piecewise.py from:

if not isinstance(variable, Variable):

to

if not isinstance(variable, Expression):

I can't find any information on this in the docs, is it intentional? If so, how can we solve the problem in the notebook and can we improve the type hints for this function?

Thanks,

Luca

[Michel Bierlaire]

Hi Luca,

I decided to restrict the use to variables in order to avoid meaningless specifications when the expression is general.
The way to go is to define TRAIN_COST_SCALED as a new variable in the database, using pandas, or using define_variable.
https://biogeme.epfl.ch/sphinx/code/biogeme/database.html#biogeme.database.Database.define_variable

It is indeed not properly documented. I'll fix that...

Thanks,

Michel

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Michel Bierlaire
Transport and Mobility Laboratory
School of Architecture, Civil and Environmental Engineering
EPFL - Ecole Polytechnique Fédérale de Lausanne
http://transp-or.epfl.ch
http://people.epfl.ch/michel.bierlaire