Ventana software support forum

I'm modelling spatial effects of automated vehicles in Vensim DSS. In the population submodel I am reallocating migrating population within the city of Copenhagen according to their respective attractiveness with the allocate available function. When running the model, the following error message displays: For example: Allocation function failed to converge computing - Entering population- at time (=for example 2030). This happens for all priority types and at several times during the simulation.

It doesn't stop the model from running, but I can't figure out what this Error message tries to tell me. Do you have experience with this message and is there a way to work it out?

I think we'd need to see the model, or a small submodel that replicates the problem.

One possible cause might be having a lot of "distant" priorities with a narrow width parameter, though that shouldn't be a problem with a smooth shape parameter (type 3, Normal). Another possibility might be large differences (orders of magnitude) in the range of priorities.

Dear tomfid,

Thanks for the reply, unfortunately I am not yet able to upload the entire model. My question has been answered, as I did not know what the error message was trying to tell me. Indeed there are large differences in the range of priorities. By either setting the width wider or by normalizing the priorities the allocation function works fine again. Now I know how to solve the error.

Best regards,

mfl

tomfid wrote: ↑Tue Jan 23, 2018 3:30 pm One possible cause might be having a lot of "distant" priorities with a narrow width parameter, though that shouldn't be a problem with a smooth shape parameter (type 3, Normal). Another possibility might be large differences (orders of magnitude) in the range of priorities.

Hi, I also have this problem, it prompts an error, but the result can be obtained. According to your suggestion, I increased the width of the requirement and changed the type to 3, which really no longer prompted this question. However, I would like to ask how to understand this problem from changing these parameters?

The allocation is essentially creating an aggregate supply and demand curve, then finding the intersection.
https://www.vensim.com/documentation/24325.html

If the distance between the priorities is much greater than the width, you get curves with intermittent flat spots. That makes it hard for the algorithm to find the intersection, because there's no gradient to follow in the flat areas.