Modeling sigma in brms using mean

[bdeonovic]

Seems similar to

Brms package in R. Error: The following variables can neither be found in 'data' nor in 'data2'

I think you need those unknowns in the priors. So I have a model like this: brm(bf(y ~ a*x^2 + b*x + c, a + b + c ~ 1, nl = TRUE), data = dat2, prior = prior2) and prior2 looks like this prior2 <- prior(normal(0,1), nlpar = "a") + prior(normal(0, 2), nlpar = "b") + prior(normal(0, 2), nlpar = "c") Is that what you are talking about?