Help with error "Floating Point"

[nathalia.tonini]

Hello everyone,

In my most recent project I am investigating the relationship between individual behavior and the modal choice to assess the impact of public policies on urban mobility.

Basing on Bajracharya's model (http://www.igi-global.com/article/publi ... car/150477), I'm using Systems Dynamics to explain the causal variables of modal choice and evaluate the impact of the Brazilian Urban Mobility Policy on the individual choice of transportation mode.

The model (attached) proposes the dynamics of the use of the private car (CP) and the public transport (TP), presenting the proportion of modal participation of the private car. Note: variable names are in Portuguese.

I am using VENSIM PLE; however, when I simulate my model, I get the error "Floating Point" in the variable "Proporção de Viagens TP" at time 9.25.
I tested the same model in other software and simulated normally.

Can anyone help me find the reason for this error to occur?
I appreciate any help.

Regards,
Nathalia

[tomfid]

The way to find the answer is to trace the causes of "Proporção de Viagens TP." See for example https://www.vensim.com/documentation/20440.htm or http://vensim.com/causal-tracing-in-vensim/.

You'll find quickly that "Uso Total do TP" goes negative very quickly. There's clearly a formulation error in the CP-TP stocks loop. The implementation of the model must be different from the version you tested in some other software.

[tomfid]

This model would really benefit from having units defined and balanced. That might reveal the error.