ApolloChoiceModelling forum

Hi everyone,
Is it possible to restrict the values of a parameter to be estimated in a range? Ie to specify min and max values?
I'm asking this question because I get trouble with the estimation of a model with a power function.

My model is as follows:

U1=ASC1+alpha_cost*COST1+alpha1_time*TIME1+alpha_var*VAR1^delta
U2=ASC2+alpha_cost*COST2+alpha2_time*TIME2+alpha_var*VAR2^delta
U3=ASC3+alpha_cost*COST3+alpha3_time*TIME3+alpha_var*VAR3^delta

It converges and I get consistent results with Biogeme but it does not converge with Apollo. I tried to change the initial values but the problem remains.
If I omit delta, then it works. If I set for instance delta=0.5 and consider this parameter as fixed, then it also works.

Thank you for your help.

Solveigh

Hi

in general, constrained estimation is not a good idea as your estimates will likely just go to the bounds if the true value is outside the bounds.

Can you be more specific in relation to what happens? Can you show us the results and the Biogeme ones?

Stephane