Monthly Math development meeting: 05/20/2021, 10 am EDT

Hey all, we’ve been having monthly Math meetings on the third Thursday of the month. The next one is tomorrow, May 20, 2021, at 10 am EDT.

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.

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cc: @bbbales2, @rok_cesnovar, @stevebronder , @storopoli, @charlesm93, @spinkney, @charlesm93, @wds15

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Thanks! See you guys tomorrow!

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I would like to talk about returning prim types from rev functions that always have adjoint equal to 0. see Make functions that do not propagate derivatives return prim types by t4c1 · Pull Request #2473 · stan-dev/math · GitHub

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@storopoli, @wds15 are here.

@stevebronder joined.

@tadej is on too.

We’re talking about @tadej’s agenda point, PR: Make functions that do not propagate derivatives return prim types by t4c1 · Pull Request #2473 · stan-dev/math · GitHub

We spent a while talking about this… the pros and cons.

If we did include this, we would bump major versions: the use of auto could break since a function that returns a var now could return double instead.

The other downside is that it changes the design of the Math functions… right now, the return type is the always promoted type (almost always now with the Eigen expressions). But with this change, a developer would need to think of when it is not.

Right now, we can hold the PR until we’re ready for a backwards incompatible change.

We talked about a few other things… the new ODE solver, Mac processors, speed regression.

Meeting adjourned. Thanks all!