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Example models for Stan
http://mc-stan.org/
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Lotka-Volterra example not running #161

Open josswright opened 4 years ago

josswright commented 4 years ago

I just went through the Lotka-Volterra example via the .Rmd, and also by pulling out the R code directly. There's a bug that seems to come from the creation of the lynx_hare_data list without named elements.

With the current specification (line 527 of the lotka-volterra-predator-prey.Rmd ):

lynx_hare_data <- list(N, ts, y_init, y)

I get the following error when trying to fit the model:

Error in new_CppObject_xp(fields$.module, fields$.pointer, ...) : 
Exception: variable does not exist; processing stage=data initialization; variable name=N; base type=int  (in 'model328085d4d633a_lotka_volterra' at line 21)

failed to create the sampler; sampling not done

This can be fixed by naming the list elements appropriately:

lynx_hare_data <- list(N=N, ts=ts, y_init=y_init, y=y)

I'm assuming that this must be a changed behaviour in some recent version of rstan?

bob-carpenter commented 4 years ago

Thanks for reporting and providing the appropriate patch. Behavior may have changed, but I don't know how this ran before. RStan can just read out of the environment, so that might've been happening somewhere before.

I just patched and added an acknowledgement.