# Interfaces

**URL:** https://discourse.mc-stan.org/c/interfaces/5.md

[Latest](https://discourse.mc-stan.org/latest.md) · [Categories](https://discourse.mc-stan.org/categories.md) · [Tags](https://discourse.mc-stan.org/tags.md)

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## [About the Interfaces category](https://discourse.mc-stan.org/t/about-the-interfaces-category/16)

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**Author:** [@betanalpha](https://discourse.mc-stan.org/u/betanalpha)\
**Replies:** 0

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This category is for questions regarding the installation and use of the Stan interfaces.

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## [Help testing brms pr for sum-to-zero and partial centering](https://discourse.mc-stan.org/t/help-testing-brms-pr-for-sum-to-zero-and-partial-centering/41542)

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**Author:** [@spinkney](https://discourse.mc-stan.org/u/spinkney)\
**Replies:** 43\
**Last updated:** [September 18, 2026, 9:39am UTC](https://discourse.mc-stan.org/t/help-testing-brms-pr-for-sum-to-zero-and-partial-centering/41542 "2026-09-18T09:39:05Z")

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Hi brms users, I’m hoping to get eyes on this pr Add fast sum-to-zero parameterizations for group effects by spinkney · Pull Request #1919 · paul-buerkner/brms · GitHub Warnings, it is large and it is AI generated becau…

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## [RStan compilation error with R 4.6.1, Rtools45 and rstan 2.39](https://discourse.mc-stan.org/t/rstan-compilation-error-with-r-4-6-1-rtools45-and-rstan-2-39/41589)

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**Author:** [@Marta](https://discourse.mc-stan.org/u/Marta)\
**Replies:** 4\
**Last updated:** [September 12, 2026, 9:07am UTC](https://discourse.mc-stan.org/t/rstan-compilation-error-with-r-4-6-1-rtools45-and-rstan-2-39/41589 "2026-09-12T09:07:05Z")

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Hello, I am having a compilation problem with RStan on Windows and would appreciate your help identifying the cause. My current setup is: Windows 10 Pro R 4.6.1 (2026-06-24 ucrt) Rtools45 GCC 14.3.0 rsta…

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## [Understanding sample\_new\_levels = "uncertainty", "gaussian", and "old\_levels"](https://discourse.mc-stan.org/t/understanding-sample-new-levels-uncertainty-gaussian-and-old-levels/7828)

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**Author:** [@AntonioV](https://discourse.mc-stan.org/u/AntonioV)\
**Replies:** 19\
**Last updated:** [September 7, 2026, 12:27pm UTC](https://discourse.mc-stan.org/t/understanding-sample-new-levels-uncertainty-gaussian-and-old-levels/7828 "2026-09-07T12:27:17Z")

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The documentation for brms::extract\_draws() says this about the sample\_new\_levels option: Indicates how to sample new levels for grouping factors specified in re\_formula. This argument is only relevant if newdata is pr…

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## [Shape constrained (e.g., monotonic) smooths in brms](https://discourse.mc-stan.org/t/shape-constrained-e-g-monotonic-smooths-in-brms/7128)

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**Author:** [@tiflo](https://discourse.mc-stan.org/u/tiflo)\
**Replies:** 17\
**Last updated:** [September 4, 2026, 8:56am UTC](https://discourse.mc-stan.org/t/shape-constrained-e-g-monotonic-smooths-in-brms/7128 "2026-09-04T08:56:02Z")

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I was delighted to see that brms allows shape constrained smooths as from the scam package as part of its formula syntax. However, the post-processing such as marginal\_effects() does not seem to work. I found this old po…

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## [Saving and sharing an rstan model fit](https://discourse.mc-stan.org/t/saving-and-sharing-an-rstan-model-fit/1059)

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**Author:** [@jeremy.koster](https://discourse.mc-stan.org/u/jeremy.koster)\
**Replies:** 5\
**Last updated:** [August 24, 2026, 7:01am UTC](https://discourse.mc-stan.org/t/saving-and-sharing-an-rstan-model-fit/1059 "2026-08-24T07:01:57Z")

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This might be a basic question, but a search on relevant terms did not reveal a discussion. Apologies if I missed anything. I have estimated a model with rstan, and I would like to save the model fit object to send to …

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## [Unusually slow GPU (OpenCL) vs CPU sampling times in blavaan/cmdstanr on MareNostrum 5](https://discourse.mc-stan.org/t/unusually-slow-gpu-opencl-vs-cpu-sampling-times-in-blavaan-cmdstanr-on-marenostrum-5/41520)

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**Author:** [@Sinval](https://discourse.mc-stan.org/u/Sinval)\
**Replies:** 2\
**Last updated:** [August 17, 2026, 11:57am UTC](https://discourse.mc-stan.org/t/unusually-slow-gpu-opencl-vs-cpu-sampling-times-in-blavaan-cmdstanr-on-marenostrum-5/41520 "2026-08-17T11:57:10Z")

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I am encountering a severe performance degradation when using the GPU backend compared to the CPU in Bayesian SEM simulations via blavaan and cmdstanr. The GPU OpenCL sampling times are significantly slower than the CPU …

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## [Posterior distribution and heterogeneity in Bayesian three-level meta-analysis with brms](https://discourse.mc-stan.org/t/posterior-distribution-and-heterogeneity-in-bayesian-three-level-meta-analysis-with-brms/41451)

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**Author:** [@Yuanyuan](https://discourse.mc-stan.org/u/Yuanyuan)\
**Replies:** 0\
**Last updated:** [July 21, 2026, 10:29am UTC](https://discourse.mc-stan.org/t/posterior-distribution-and-heterogeneity-in-bayesian-three-level-meta-analysis-with-brms/41451 "2026-07-21T10:29:36Z")

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Hi, As a beginner, I am trying to do a Bayesian three-level meta-analysis with brms. Following the https://doing-meta.guide/bayesian-ma , here is the code for my main model. #Main model main.model \<- brm(yi|se(seTE)~ …

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## [Lognormal family in brms](https://discourse.mc-stan.org/t/lognormal-family-in-brms/41429)

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**Author:** [@Hunter24](https://discourse.mc-stan.org/u/Hunter24)\
**Replies:** 4\
**Last updated:** [July 16, 2026, 6:25pm UTC](https://discourse.mc-stan.org/t/lognormal-family-in-brms/41429 "2026-07-16T18:25:17Z")

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I simulated lognormal data, where the variation on the log scale is constant which I believe represents the lognormal family assumptions in brms. When I simulated this data I recovered all parameters almost exactly, but…

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## ["get\_prior() shows only one group random intercept prior when using gr(by = ...), shouldn't there be two as this model assumes groups being drawn from separate distributions?"](https://discourse.mc-stan.org/t/get-prior-shows-only-one-group-random-intercept-prior-when-using-gr-by-shouldnt-there-be-two-as-this-model-assumes-groups-being-drawn-from-separate-distributions/41428)

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**Author:** [@hunter\_warick](https://discourse.mc-stan.org/u/hunter_warick)\
**Replies:** 0\
**Last updated:** [July 8, 2026, 7:53am UTC](https://discourse.mc-stan.org/t/get-prior-shows-only-one-group-random-intercept-prior-when-using-gr-by-shouldnt-there-be-two-as-this-model-assumes-groups-being-drawn-from-separate-distributions/41428 "2026-07-08T07:53:22Z")

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Short summary of the problem brm.formula.1 \<- bf( y ~ 0 + group+ # Group-specific independent random intercepts (1 | gr(ID, by = group)), sigma ~ 0 + group ) prior\_1 \<- # coefficients prior(normal(l…

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## [New loo package CRAN release v.2.10.0](https://discourse.mc-stan.org/t/new-loo-package-cran-release-v-2-10-0/41400)

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**Author:** [@avehtari](https://discourse.mc-stan.org/u/avehtari)\
**Replies:** 3\
**Last updated:** [June 30, 2026, 8:13pm UTC](https://discourse.mc-stan.org/t/new-loo-package-cran-release-v-2-10-0/41400 "2026-06-30T20:13:35Z")

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There is a new loo package CRAN release v2.10.0 with the most important new feature being new loo\_compare() output with columns p\_worse, diag\_diff and diag\_elpd, based on paper “Uncertainty in Bayesian leave-one-out cro…

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## [Cannot install Cmdstan due to Windows 11 permissions issue](https://discourse.mc-stan.org/t/cannot-install-cmdstan-due-to-windows-11-permissions-issue/41382)

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**Author:** [@qdread](https://discourse.mc-stan.org/u/qdread)\
**Replies:** 1\
**Last updated:** [June 26, 2026, 6:33pm UTC](https://discourse.mc-stan.org/t/cannot-install-cmdstan-due-to-windows-11-permissions-issue/41382 "2026-06-26T18:33:35Z")

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Hello, I am a Stan user who has to use a work PC that is configured with various restrictions. I have had issues installing Cmdstan in the past ( Windows 11 cmdstan installation issue: Architecture not detected, related …

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## [Why does changing the reference level wildly change the predicted probabilities?](https://discourse.mc-stan.org/t/why-does-changing-the-reference-level-wildly-change-the-predicted-probabilities/41399)

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**Author:** [@FeliOtte](https://discourse.mc-stan.org/u/FeliOtte)\
**Replies:** 1\
**Last updated:** [June 26, 2026, 2:21pm UTC](https://discourse.mc-stan.org/t/why-does-changing-the-reference-level-wildly-change-the-predicted-probabilities/41399 "2026-06-26T14:21:31Z")

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Hello everyone, I’m having some modelling issues and I’m hoping the answer to the question above might help. I am running a multinomial/categorical model in brms and am getting results that do not make sense for my data…

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## [Race conditions between independent cmdstan model runs](https://discourse.mc-stan.org/t/race-conditions-between-independent-cmdstan-model-runs/30918)

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**Author:** [@alison](https://discourse.mc-stan.org/u/alison)\
**Replies:** 8\
**Last updated:** [June 25, 2026, 4:47pm UTC](https://discourse.mc-stan.org/t/race-conditions-between-independent-cmdstan-model-runs/30918 "2026-06-25T16:47:34Z")

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Dear all, I am experiencing what looks a lot to me like some kind of race condition / interaction between independent cmdstan model runs (via cmdstanr) when fitting several models on an HPC cluster. The story is as foll…

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## [Assessing influence of population-level predictors on one specific trial](https://discourse.mc-stan.org/t/assessing-influence-of-population-level-predictors-on-one-specific-trial/41396)

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**Author:** [@IreneSophia](https://discourse.mc-stan.org/u/IreneSophia)\
**Replies:** 1\
**Last updated:** [June 25, 2026, 9:00am UTC](https://discourse.mc-stan.org/t/assessing-influence-of-population-level-predictors-on-one-specific-trial/41396 "2026-06-25T09:00:54Z")

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I have an experimental design with one between-subjects factor (gender, 2 levels) and one within-subjects factor (cond, 2 levels). Each subject encounters multiple trials. The data is ordinal and I am using brms to const…

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## [Compile Stan model in Shiny App?](https://discourse.mc-stan.org/t/compile-stan-model-in-shiny-app/10022)

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**Author:** [@winterstat](https://discourse.mc-stan.org/u/winterstat)\
**Replies:** 22\
**Last updated:** [June 23, 2026, 11:51pm UTC](https://discourse.mc-stan.org/t/compile-stan-model-in-shiny-app/10022 "2026-06-23T23:51:59Z")

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Hello, I hope this is the place to ask this. Let me know if I need to go elsewhere! I’m trying to run rstan in a shiny app I’m creating. It runs fine locally, but then when I deploy it to shinyapps.io, I seem unable to …

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## [Understanding the Likelihood Model for the Cox Family in brms](https://discourse.mc-stan.org/t/understanding-the-likelihood-model-for-the-cox-family-in-brms/40622)

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**Author:** [@kaybenleroll](https://discourse.mc-stan.org/u/kaybenleroll)\
**Replies:** 5\
**Last updated:** [June 16, 2026, 8:50pm UTC](https://discourse.mc-stan.org/t/understanding-the-likelihood-model-for-the-cox-family-in-brms/40622 "2026-06-16T20:50:28Z")

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I am trying to understand the basic approach of the cox() family in brms. My understanding was that the idea is to model the baseline rate as a spline using the spline2 package, and then the covariates are proportional h…

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## [PyStan and PyCharm](https://discourse.mc-stan.org/t/pystan-and-pycharm/6487)

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**Author:** [@DjentMachine](https://discourse.mc-stan.org/u/DjentMachine)\
**Replies:** 21\
**Last updated:** [May 31, 2026, 9:47pm UTC](https://discourse.mc-stan.org/t/pystan-and-pycharm/6487 "2026-05-31T21:47:09Z")

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Hello all, I have recently trying to use PyStan in Windows and found out it’s installation is more difficult than I thought. I normally use PyCharm as my IDE and was hopping to use PyStan with it. However, most advice I…

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## [Calculate indirect effects for a longitudinal Gaussian Process mediation model](https://discourse.mc-stan.org/t/calculate-indirect-effects-for-a-longitudinal-gaussian-process-mediation-model/41294)

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**Author:** [@drnight](https://discourse.mc-stan.org/u/drnight)\
**Replies:** 1\
**Last updated:** [May 25, 2026, 12:24pm UTC](https://discourse.mc-stan.org/t/calculate-indirect-effects-for-a-longitudinal-gaussian-process-mediation-model/41294 "2026-05-25T12:24:09Z")

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Hello, I am running a longitudinal mediation model with both the independent and the mediatior variables being time-varying (for 6 time points), using Gaussian Process in brms. Would be grateful if anyone could help me…

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## [Rstan process on remote desktop stops when I'm disconnected](https://discourse.mc-stan.org/t/rstan-process-on-remote-desktop-stops-when-im-disconnected/41215)

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**Author:** [@bugay-yildirim](https://discourse.mc-stan.org/u/bugay-yildirim)\
**Replies:** 6\
**Last updated:** [May 20, 2026, 7:24am UTC](https://discourse.mc-stan.org/t/rstan-process-on-remote-desktop-stops-when-im-disconnected/41215 "2026-05-20T07:24:22Z")

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Hello everyone, I am running a model using rstan in RStudio on a remote Windows laptop that is connected to my university’s server. I access it from my local computer using Windows Remote Desktop Connection (RDP) over m…

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## [Longitudinal Mediation with only two time points](https://discourse.mc-stan.org/t/longitudinal-mediation-with-only-two-time-points/41239)

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**Author:** [@drnight](https://discourse.mc-stan.org/u/drnight)\
**Replies:** 0\
**Last updated:** [May 15, 2026, 9:01pm UTC](https://discourse.mc-stan.org/t/longitudinal-mediation-with-only-two-time-points/41239 "2026-05-15T21:01:07Z")

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I am doing longitudinal mediation analysis with brms. Previous suggestions include the use of splines and Gaussian process. However, because I’m only considering two time points (baseline and end-of-treatment), I am not …

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## [Database Ingest into Stan](https://discourse.mc-stan.org/t/database-ingest-into-stan/41238)

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**Author:** [@s.maskell](https://discourse.mc-stan.org/u/s.maskell)\
**Replies:** 2\
**Last updated:** [May 15, 2026, 3:42pm UTC](https://discourse.mc-stan.org/t/database-ingest-into-stan/41238 "2026-05-15T15:42:15Z")

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We have some work to develop a Stan model. The data we are considering are relatively numerous (potentially more than 300 million data) and natively stored in a postgres database, which is continually evolving such that …

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## [Evidence ratios when using default priors](https://discourse.mc-stan.org/t/evidence-ratios-when-using-default-priors/4847)

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**Author:** [@ivan\_grahek](https://discourse.mc-stan.org/u/ivan_grahek)\
**Replies:** 12\
**Last updated:** [April 29, 2026, 4:12am UTC](https://discourse.mc-stan.org/t/evidence-ratios-when-using-default-priors/4847 "2026-04-29T04:12:20Z")

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Hi, I have fitted a multilevel model with an interaction between three factors (3X2X2 factorial design, predicting EEG amplitudes with several experimental conditions, i.e., categorical variables) with varying slopes an…

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## [Timeline for Rstan update on CRAN](https://discourse.mc-stan.org/t/timeline-for-rstan-update-on-cran/41038)

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**Author:** [@novice](https://discourse.mc-stan.org/u/novice)\
**Replies:** 5\
**Last updated:** [April 28, 2026, 9:01am UTC](https://discourse.mc-stan.org/t/timeline-for-rstan-update-on-cran/41038 "2026-04-28T09:01:39Z")

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I’m writing an R package that relies on Rstan and plan to put it on CRAN once an accompanying article has been published. I want use some functionality from Stan 2.36 (sum-to-zero-vectors), but CRAN is still at Rstan ver…

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## [Stan.jl v10.8.4 Released](https://discourse.mc-stan.org/t/stan-jl-v10-8-4-released/41079)

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**Author:** [@bparbhu](https://discourse.mc-stan.org/u/bparbhu)\
**Replies:** 1\
**Last updated:** [April 28, 2026, 2:52am UTC](https://discourse.mc-stan.org/t/stan-jl-v10-8-4-released/41079 "2026-04-28T02:52:30Z")

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Stan.jl v10.8.4 Released — CmdStan 2.37 Support and Ecosystem Refresh We’re happy to announce the release of Stan.jl v10.8.4. This release brings the Stan.jl ecosystem to CmdStan 2.37, giving the Julia community access…

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## [Mean-centered variables in brms](https://discourse.mc-stan.org/t/mean-centered-variables-in-brms/41064)

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**Author:** [@REYZ](https://discourse.mc-stan.org/u/REYZ)\
**Replies:** 4\
**Last updated:** [April 24, 2026, 1:43pm UTC](https://discourse.mc-stan.org/t/mean-centered-variables-in-brms/41064 "2026-04-24T13:43:27Z")

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Hello! I am trying to model a behavioral task using brms. There are two independent variables (each with two levels), and I am interested mostly in the interaction effect (var1\*var2). Task responses were made on a discr…

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## [Proposal for moving stan\_surv() to a separate package](https://discourse.mc-stan.org/t/proposal-for-moving-stan-surv-to-a-separate-package/41020)

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**Author:** [@ericnovik](https://discourse.mc-stan.org/u/ericnovik)\
**Replies:** 7\
**Last updated:** [April 12, 2026, 11:17pm UTC](https://discourse.mc-stan.org/t/proposal-for-moving-stan-surv-to-a-separate-package/41020 "2026-04-12T23:17:00Z")

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Hello All, I would like to propose moving stan\_surv() (Survival functionality) from rstanarm to a separate package, say SurvivalStan. The reasons are as follows: At this point, it seems unlikely that the survival br…

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## [Add\_criterion applied to a model produced by brm()](https://discourse.mc-stan.org/t/add-criterion-applied-to-a-model-produced-by-brm/41037)

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**Author:** [@JKingston](https://discourse.mc-stan.org/u/JKingston)\
**Replies:** 3\
**Last updated:** [April 9, 2026, 3:26pm UTC](https://discourse.mc-stan.org/t/add-criterion-applied-to-a-model-produced-by-brm/41037 "2026-04-09T15:26:43Z")

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Please share your Stan program and accompanying data if possible. I am trying to use add\_criterion() to add “loo” to a model created with brm(), so that I can use loo\_compare() to compared models. add\_criterion() appea…

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## [Pkgbuild::compile\_dll() on previously working rstantools-based package fails with "file too big" error](https://discourse.mc-stan.org/t/pkgbuild-compile-dll-on-previously-working-rstantools-based-package-fails-with-file-too-big-error/21938)

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**Author:** [@ebuhle](https://discourse.mc-stan.org/u/ebuhle)\
**Replies:** 27\
**Last updated:** [April 5, 2026, 11:00am UTC](https://discourse.mc-stan.org/t/pkgbuild-compile-dll-on-previously-working-rstantools-based-package-fails-with-file-too-big-error/21938 "2026-04-05T11:00:38Z")

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I’m encountering a new (to me) problem when trying to compile my Stan-dependent packages built with rstantools in RStudio. My workflow, following the vignette, has been: pkgbuild::compile\_dll() roxygen2::roxygenize() de…

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## [Cmdstan installation fails on linux - issue with tbb?](https://discourse.mc-stan.org/t/cmdstan-installation-fails-on-linux-issue-with-tbb/31125)

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**Author:** [@Unlearned5341](https://discourse.mc-stan.org/u/Unlearned5341)\
**Replies:** 4\
**Last updated:** [April 2, 2026, 10:43am UTC](https://discourse.mc-stan.org/t/cmdstan-installation-fails-on-linux-issue-with-tbb/31125 "2026-04-02T10:43:28Z")

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I wish my first post would not be about an installation issue… but here I am! Yesterday, I upgraded my linux system from Fedora 37 to Fedora 38 and noticed I could not compile Stan models with cmdstanr anymore. I have tr…

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