I have run two complex multivariate models following this tutorial: https://cran.r-project.org/web/packages/brms/vignettes/brms_multivariate.html. The models follow this format:

```
f1 = as.formula('y1~1+var1+var2+var3+(1+var1+var2+var3|GroupID)')
f2 = as.formula('y2~1+var1+var2+var3+(1+var1+var2+var3|GroupID)')
f3 = as.formula('y1~1+var1+var2+(1+var1+var2+|GroupID)')
f4 = as.formula('y2~1+var1+var2+(1+var1+var2+|GroupID)')
model_of_interest = brm(f1+f2,data=df,iter=6000,chains=4,cores=4,family="gaussian",control=list(adapt_delta=0.9),save_all_pars=TRUE)
null_model = brm(f3+f4,data=df,iter=6000,chains=4,cores=4,family="gaussian",control=list(adapt_delta=0.9),save_all_pars=TRUE)
```

and I now want to compute `loo()`

for each and compare using `loo_compare()`

. Using this tutorial as a guide http://mc-stan.org/loo/articles/loo2-example.html, I compute `loo`

as follows:

```
loo1 <- loo(model_of_interest, moment_match=TRUE)
loo2 <- loo(null_model, moment_match=TRUE)
```

However, before I can enter this into `loo_compare()`

I get this error for both `loo1`

and `loo2`

:

Error in .update_pars(x, upars = upars, …) :

length(new_samples) == nrow(pars) is not TRUE

Error: Moment matching failed. Perhaps you did not set ‘save_all_pars’ to TRUE when fitting your model?

I am confused because I have definitely set `save_all_pars=TRUE`

in both model fits, and I can’t seem to find helpful guidance online about how to solve this. I am using R version 4.0.2. I appreciate any advice, thanks very much.