stan-dev/stan

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Stan development repository. The master branch contains the current release. The develop branch contains the latest stable development. See the Developer Process Wiki for details.

Stars: 2.8k
Forks: 388
Open beginner issues: 0
Indexed issues: 137
Avg merge: 2d 17h
Merged PRs (30d): 15

Dominant language: C++
License: BSD-3-Clause
Last GitHub push: Sep 16, 2026
Latest indexed: Sep 19, 2026
Contributing guide: Contributing guide
Code of conduct: No code of conduct
Beginner labels: good first issue help wanted

Beginner friendly Everything

Open All

137 open issues indexed

User defined gradients Open

Difficulty 5/5 Over a week Newbie friendliness 35/100

stan-dev/stan#3432 · 9 comments · Opened Sep 11, 2026
Newton optimizer produces NaN parameters for a target with a flat direction, no error raised Open

Difficulty 3/5 1-2 days Newbie friendliness 66/100

stan-dev/stan#3425 · 2 comments · Opened Sep 2, 2026
Improve allocation behavior in NUTS Open

algorithm code cleanup help wanted

Difficulty 4/5 3-5 days Newbie friendliness 38/100

stan-dev/stan#3414 · 1 comment · Opened Aug 24, 2026
Include (unconstrained) parameter names along with the inverse metric? Open

good first issue i/o interface

Difficulty 3/5 1-2 days Newbie friendliness 65/100

stan-dev/stan#3398 · 4 comments · Opened Jul 21, 2026
base_nuts.hpp:110 — Unnecessary .transpose() on column vector Open

Difficulty 1/5 Under an hour Newbie friendliness 86/100

stan-dev/stan#3381 · Opened Apr 17, 2026
Additional services missing timing information in csv Open

Difficulty 3/5 1-2 days Newbie friendliness 55/100

stan-dev/stan#3376 · Opened Apr 9, 2026
Lift the "(Transformed) parameters cannot be integers" restriction Open

Difficulty 5/5 Over a week Newbie friendliness 30/100

stan-dev/stan#3363 · 5 comments · Opened Oct 10, 2025
ODE solvers unnecessarily disallow `initial_time == times[1]` Open

Difficulty 3/5 1-2 days Newbie friendliness 35/100

stan-dev/stan#3360 · Opened Oct 8, 2025
write transformed data along with posterior sample Open

feature i/o interface

Difficulty 5/5 Over a week Newbie friendliness 25/100

stan-dev/stan#3349 · 2 comments · Opened Jun 16, 2025
Services/algorithms: Additional structured_writer for timing information Open

i/o interface

Difficulty 5/5 Over a week Newbie friendliness 25/100

stan-dev/stan#3340 · 1 reaction · Opened Mar 21, 2025
Feature request: Add timestamps to sample progress Open

Difficulty 4/5 3-5 days Newbie friendliness 38/100

stan-dev/stan#3339 · 8 comments · 1 reaction · Opened Mar 12, 2025
Feature request: Can we have a more compact output formats than CSV such as Parquet? Open

i/o

Difficulty 5/5 Over a week Newbie friendliness 28/100

stan-dev/stan#3332 · 1 comment · Opened Feb 17, 2025
Improve error messaging at: Error evaluating initial BFGS point. Open

Difficulty 4/5 3-5 days Newbie friendliness 35/100

stan-dev/stan#3327 · 3 comments · Opened Jan 17, 2025
FEATURE REQUEST: Can we have native support for ragged arrays? Open

Difficulty 5/5 Over a week Newbie friendliness 25/100

stan-dev/stan#3326 · 4 comments · Opened Jan 8, 2025
ADVI: Option to save family parameters to JSON Open

i/o interface

Difficulty 4/5 3-5 days Newbie friendliness 45/100

stan-dev/stan#3315 · Opened Nov 18, 2024
Modify the opitimization line search to not return a point with non-finite gradient Open

stan-dev/stan#3306 · 1 comment · 1 assignee · Opened Jul 31, 2024
Add boolean-based indexing (e.g., `Y[Z == 1]`) Open

Difficulty 4/5 3-5 days Newbie friendliness 35/100

stan-dev/stan#3300 · 11 comments · 4 reactions · Opened Jul 16, 2024
Review the Issues list please? Open

Difficulty 5/5 Over a week Newbie friendliness 15/100

stan-dev/stan#3297 · 2 comments · Opened Jun 30, 2024
FR: `model_base` methods - use `Eigen::Ref<Eigen::VectorXd>` Open

Difficulty 4/5 3-5 days Newbie friendliness 35/100

stan-dev/stan#3289 · 1 reaction · Opened May 23, 2024
report condition number of metric for HMC adaptive samplers Open

new function

Difficulty 5/5 Over a week Newbie friendliness 25/100

stan-dev/stan#3280 · 4 comments · Opened Apr 15, 2024
Move from int to long int? Open

i/o

Difficulty 5/5 Over a week Newbie friendliness 20/100

stan-dev/stan#3277 · 3 comments · 1 reaction · Opened Apr 1, 2024
Too loose ASSERT_NEAR and wrong test values in compute_potential_scale_reduction_test.cpp Open

Difficulty 2/5 1-3 hours Newbie friendliness 50/100

stan-dev/stan#3273 · 3 comments · Opened Feb 26, 2024
`install-tbb.bat` fails on windows Open

Difficulty 1/5 Under an hour Newbie friendliness 35/100

stan-dev/stan#3245 · Opened Dec 2, 2023
Print statements inside a model are buffered into a stringstream and only printed when log_prob returns Open

Difficulty 4/5 3-5 days Newbie friendliness 35/100

stan-dev/stan#3233 · Opened Oct 4, 2023
Infinite loop in `WolfLSZoom` when using stan for optimization Open

Difficulty 4/5 3-5 days Newbie friendliness 35/100

stan-dev/stan#3229 · 8 comments · Opened Sep 11, 2023
Use "approximate" instead of "experimental" for Pathfinder and ADVI descriptions Open

documentation interface

Difficulty 4/5 3-5 days Newbie friendliness 38/100

stan-dev/stan#3207 · Opened Jul 13, 2023
promote logger and writer mock objects from pathfinder utils Open

code cleanup feature good first issue testing

Difficulty 3/5 1-2 days Newbie friendliness 35/100

stan-dev/stan#3194 · 6 comments · Opened Jun 4, 2023
*_rng() functions that match all existing signatures available for corresponding *_lpdf() functions Open

Difficulty 5/5 Over a week Newbie friendliness 30/100

stan-dev/stan#3185 · 1 comment · Opened Apr 30, 2023
virtual declarations missing for `get_constrained_sizedtypes()` and `get_constrained_sizedtypes()` in `model_base` Open

feature i/o language

Difficulty 2/5 1-3 hours Newbie friendliness 35/100

stan-dev/stan#3175 · 9 comments · Opened Mar 24, 2023
Replacing `llt` with `ldlt` decomposition in the Laplace approximation Open

Difficulty 2/5 1-3 hours Newbie friendliness 45/100

stan-dev/stan#3156 · Opened Dec 1, 2022
Improve step size adaptation target Open

algorithm documentation

Difficulty 5/5 Over a week Newbie friendliness 18/100

stan-dev/stan#3105 · 17 comments · 4 reactions · Opened Feb 22, 2022
[FR] low rank HMC? Open

Difficulty 5/5 Over a week Newbie friendliness 25/100

stan-dev/stan#3102 · 2 comments · 2 reactions · Opened Feb 17, 2022
Allow _lupdf and _lupmf functions in the transformed parameters block Open

Difficulty 4/5 3-5 days Newbie friendliness 35/100

stan-dev/stan#3094 · 4 comments · Opened Dec 23, 2021
Some computations not included in reported total time of output CSVs Open

Difficulty 4/5 3-5 days Newbie friendliness 35/100

stan-dev/stan#3089 · 21 comments · Opened Nov 23, 2021
Instructions on how to use core Stan directly in C++ Open

documentation good first issue

Difficulty 4/5 3-5 days Newbie friendliness 35/100

stan-dev/stan#3086 · 3 comments · 2 reactions · Opened Nov 19, 2021
One redundant gradient evaluation on every iteration Open

Difficulty 5/5 Over a week Newbie friendliness 25/100

stan-dev/stan#3077 · 2 comments · Opened Oct 29, 2021
General performance improvements discussion Open

Difficulty 5/5 Over a week Newbie friendliness 18/100

stan-dev/stan#3062 · 4 comments · 1 reaction · Opened Sep 7, 2021
FR: 0_append for csvs Open

i/o

Difficulty 4/5 3-5 days Newbie friendliness 25/100

stan-dev/stan#3044 · Opened Jun 3, 2021
Offset/multiplier noncentering gets trapped at low sigma Open

Difficulty 4/5 3-5 days Newbie friendliness 38/100

stan-dev/stan#3088 · 4 comments · Opened May 7, 2021
If model evaluates at initial conditions without autodiff but fails with autodiff then the error messages are not great Open

Difficulty 4/5 3-5 days Newbie friendliness 35/100

stan-dev/stan#3034 · 10 comments · Opened Mar 31, 2021
corr_matrix of size 0 fails Open

bug

Difficulty 4/5 3-5 days Newbie friendliness 28/100

stan-dev/stan#2958 · 3 comments · Opened Sep 30, 2020
Provide access to initial values Open

feature i/o

Difficulty 4/5 3-5 days Newbie friendliness 25/100

stan-dev/stan#2950 · 11 comments · Opened Aug 8, 2020
Don't require two Stan programs to use standalone GQs (add a flag to services to turn off GQ block) Open

feature

Difficulty 4/5 3-5 days Newbie friendliness 35/100

stan-dev/stan#2934 · 4 comments · 2 reactions · Opened Jun 30, 2020
move dimension validation inside var_context Open

feature

Difficulty 5/5 Over a week Newbie friendliness 25/100

stan-dev/stan#2925 · Opened May 23, 2020
var_context builder Open

feature good first issue

Difficulty 4/5 3-5 days Newbie friendliness 30/100

stan-dev/stan#2924 · Opened May 23, 2020
Potential issues with slicing Open

Difficulty 5/5 Over a week Newbie friendliness 25/100

stan-dev/stan#2904 · 2 comments · Opened Mar 20, 2020
Adding Sparse Matrix Indexing Open

feature

stan-dev/stan#2900 · 8 comments · 2 assignees · Opened Mar 12, 2020
Doing the decomposition for every momentum draw is inefficient Open

Difficulty 3/5 1-2 days Newbie friendliness 45/100

stan-dev/stan#2881 · 12 comments · 1 reaction · Opened Jan 22, 2020
Speculative dynamic HMC Open

Difficulty 5/5 Over a week Newbie friendliness 20/100

stan-dev/stan#2818 · 38 comments · Opened Sep 12, 2019
Implement automatic selection of dense/diag metric at warmup Open

Difficulty 5/5 Over a week Newbie friendliness 25/100

stan-dev/stan#2814 · 2 comments · Opened Sep 11, 2019

stan-dev/stan

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