Error when running loo with moment_match = TRUE on rstan model from previous session

从报告中链接的 loo(fit, moment_match = TRUE) 入口点和 rstan/R/loo.R 实现开始。先保存并重新加载一个 stanfit，再调用 loo，以复现该失败，然后将其与同一 session 中的调用进行比较。完成标准是重新加载的模型能够完成 moment matching，且不会出现无效模型错误，并有一个覆盖保存并重新加载案例的回归测试。

Hi,

I'm trying to run loo with moment matching on an rstan model fit in a previous session. The stanfit object was saved using:

fit <- stan(...)
saveRDS(fit,...)

And then loaded and loo (from https://github.com/stan-dev/rstan/blob/develop/rstan/rstan/R/loo.R) was run with:

fit <- loadRDS(...)
loo(fit, moment_match = TRUE)

which throws the following error:

Error in .local(object, ...) : 
  the model object is not created or not valid
Calls: loo ... apply -> FUN -> <Anonymous> -> <Anonymous> -> .local
Execution halted

Fitting and loading are both happening on the same system (university HPC cluster). I have no problems loading the stanfit object and then running other functions on this system (running extract(fit) for example) or loading the stanfit object on my local system (Mac OS 11.2.1). This also works fine if the model is fit and then loo is run within the same session (i.e. not from a .rds file).

HPC Cluster specs:

cat /etc/*-release

Cluster Manager v9.1
slave
NAME="Red Hat Enterprise Linux"
VERSION="8.2 (Ootpa)"
ID="rhel"
ID_LIKE="fedora"
VERSION_ID="8.2"
PLATFORM_ID="platform:el8"
PRETTY_NAME="Red Hat Enterprise Linux 8.2 (Ootpa)"
ANSI_COLOR="0;31"
CPE_NAME="cpe:/o:redhat:enterprise_linux:8.2:GA"
HOME_URL="https://www.redhat.com/"
BUG_REPORT_URL="https://bugzilla.redhat.com/"

REDHAT_BUGZILLA_PRODUCT="Red Hat Enterprise Linux 8"
REDHAT_BUGZILLA_PRODUCT_VERSION=8.2
REDHAT_SUPPORT_PRODUCT="Red Hat Enterprise Linux"
REDHAT_SUPPORT_PRODUCT_VERSION="8.2"
Red Hat Enterprise Linux release 8.2 (Ootpa)
Red Hat Enterprise Linux release 8.2 (Ootpa)

R environment specs:

R version 4.1.0 (2021-05-18) -- "Camp Pontanezen"
rstan (version 2.21.2)

Thanks for your help and developing such an awesome package! If this is an rstan and not a loo problem I'm happy to move the issue there.