Monthly Math development meeting: 02/17/2021, 10 am ET

Hey all, we’ve been having monthly Math meetings on the third Thursday of the month. The next one is tomorrow, Feb 17, 2021, at 10 am!

This will last no more than one hour; if we need more time, we will schedule additional time.

This meeting is open to all those that currently contribute to the Math library or that would like to contribute to the Math library. If you’d like an invite to the Google Calendar event, please DM me with your Google handle. If you’d like to just have a copy of the event on your calendar, please use this link:

Direct Google Meet link:


  • this is a chance to collaborate and coordinate efforts. We’re expecting everyone to be kind and courteous. And patient. We have a team with diverse backgrounds.
  • impactful decisions will not be made at these meetings. That will continue to be done online on these forums. The meetings are a good time to discuss and get on the same page, but the decision making will be done online where we can include the opinions of others that can’t make the meeting.
  • important discussions that happen at the meeting will be communicated back online on these forums. If they don’t make it back here, it wasn’t important. No one will be penalized for not being present at a meeting.

If there’s anything you know you want to talk about, please post here. This is a good time to request help from others if there’s expertise that you need.


@storopoli is here. And so is @bbbales2 too.

We’re chatting about GitHub Actions and projects that @storopoli can help out with.

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@bbbales2 is walking us through Add GHA tarball builder by rok-cesnovar · Pull Request #982 · stan-dev/cmdstan · GitHub.

It builds a tarball using different branches and that’ll put together a single tarball.

Ben’s ask: he doesn’t know how this works. Can @storopoli review this?

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We’re chatting about v2.26.1.

@bbbales2 walking us through it:

  • cholesky decomposition gradients were not working in a weird situation: if you passed a matrix and the autodiff variables were not all unique, you’d have a problem.
  • bug with reduce_sum() using within reduce_sum() would cause a compiler error; interaction with Eigen expressions.
  • OpenCL distribution not accepting row vectors.
  • A lot of changes in the Math library between v2.25 vs v2.26.

I asked @bbbales2 if there’s a way to test the cholesky problem generally. Right now, it has to be checked manually.

All of us are discussing and brainstorming if there are ways to check it in an automated way.

@charlesm93 joined us too.

We’re asking whether we can make the testing more efficient.

@storopoli is showing us how the limits of GitHub actions. Every job must complete in 6 hours, every workflow action must complete in 72 hours (3 days).

@bbbales2 is talking about walking through the code, but is into limiting work in progress (which I agree with).

@rok_cesnovar joined us!

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@bbbales2 is walking us through stats from the backlog ( PRs) and asking how we can go faster.

Meeting adjourned at 11 am.