The value of `k` for when using additive models in brms

Given a model bf( y ~ s(ti)), how can i find the value of k chosen by brms(or i guess mgcv::s) ?
Looking at the generated Stan file, it appears it is passed to Stan (and not estimated by Stan). Is my understanding correct?

Thanks much

  • Operating System: Linux
  • brms Version: 2.6

It is not estimated and the default depends on how the spline is specified. Look at help(s, package = "mgcv").

Would the value of k chosen (or even the value provided, if provided) be found in the data structure returned by brm?

You may infer it from the number of columns of the Zs_* elements returned by make_standata, but this doesn’t work in the same way for all kinds of splines, so I would be careful with it.