# Articles by Bob Carpenter

### How many infectious people are likely to show up at an event?

December 22, 2020 |

Stephen Kissler and Yonatan Grad launched a Shiny app, Effective SARS-CoV-2 test sensitivity, to help you answer the question, How many infectious people are likely to show up to an event, given a screening test administered n days prior to the event? Here’s a screenshot. The app is based ...

### Probabilities for action and resistance in Blades in the Dark

July 15, 2020 |

Later this week, I’m going to be GM-ing my first session of Blades in the Dark, a role-playing game designed by John Harper. We’ve already assembled a crew of scoundrels in Session 0 and set the first score. Unlike most of the other games I’ve run, I’ve ... [Read more...]

### Drunk-under-the-lamppost testing

July 7, 2020 |

I’m writing a response here to Abraham Mathews’s post, Best practices for code review, R edition, because my comment there didn’t show up and I think the topic’s important. Mathews’s post starts out on the right track, then veers away from best practices in the ... [Read more...]

### Make Andrew happy with one simple ggplot trick

May 7, 2020 |

By default, ggplot expands the space above and below the x-axis (and to the left and right of the y-axis). Andrew has made it pretty clear that he thinks the x axis should be drawn at y = 0. To remove the extra space around the axes when you have continuous (not ... [Read more...]

### Naming conventions for variables, functions, etc.

March 11, 2020 |

The golden rule of code layout is that code should be written to be readable. And that means readable by others, including you in the future. Three principles of naming follow: 1. Names should mean something. 2. Names should be as short as possible. 3. Use your judgement to balance (1) and (2). The third […] [Read more...]

### Beautiful paper on HMMs and derivatives

December 16, 2019 |

I’ve been talking to Michael Betancourt and Charles Margossian about implementing analytic derivatives for HMMs in Stan to reduce memory overhead and increase speed. For now, one has to implement the forward algorithm in the Stan program and let Stan autodiff through it. I worked out the adjoint method (... [Read more...]

### Econometrics postdoc and computational statistics postdoc openings here in the Stan group at Columbia

November 22, 2019 |

Andrew and I are looking to hire two postdocs to join the Stan group at Columbia starting January 2020. I want to emphasize that these are postdoc positions, not programmer positions. So while each position has a practical focus, our broader goal is to carry out high-impact, practical research that pushes ... [Read more...]

### Non-randomly missing data is hard, or why weights won’t solve your survey problems and you need to think generatively

October 29, 2019 |

Throw this onto the big pile of stats problems that are a lot more subtle than they seem at first glance. This all started when Lauren pointed me at the post Another way to see why mixed models in survey data are hard on Thomas Lumley’s blog. Part of ... [Read more...]

### Seeking postdoc (or contractor) for next generation Stan language research and development

August 30, 2019 |

The Stan group at Columbia is looking to hire a postdoc* to work on the next generation compiler for the Stan open-source probabilistic programming language. Ideally, a candidate will bring language development experience and also have research interests in a related field such as programming languages, applied statistics, numerical analysis, ... [Read more...]

### Markov chain Monte Carlo doesn’t “explore the posterior”

March 25, 2019 |

First some background, then the bad news, and finally the good news. Spoiler alert: The bad news is that exploring the posterior is intractable; the good news is that we don’t need to explore all of it. Sampling to characterize the posterior There’s a misconception among Markov chain ... [Read more...]

### NYC Meetup Thursday: Under the hood: Stan’s library, language, and algorithms

January 11, 2019 |

I (Bob, not Andrew!) will be doing a meetup talk this coming Thursday in New York City. Here’s the link with registration and location and time details (summary: pizza unboxing at 6:30 pm in SoHo): Bayesian Data Analysis Meetup: Under the hood: Stan’s library, language, and algorithms After summarizing ... [Read more...]

### StanCon Helsinki streaming live now (and tomorrow)

August 30, 2018 |

We’re streaming live right now! Thursday 08:45-17:30: YouTube Link Friday 09:00-17:00: YouTube Link Timezone is Eastern European Summer Time (EEST) +0300 UTC Here’s a link to the full program [link fixed]. There have already been some great talks and they’ll all be posted with slides and runnable source ... [Read more...]

### StanCon Helsinki streaming live now (and tomorrow)

August 30, 2018 |

We’re streaming live right now! Thursday 08:45-17:30: YouTube Link Friday 09:00-17:00: YouTube Link Timezone is Eastern European Summer Time (EEST) +0300 UTC Here’s a link to the full program [link fixed]. There have already been some great talks and they’ll all be posted with slides and runnable source ... [Read more...]

### Thanks, NVIDIA

August 1, 2018 |

Andrew and I both received a note like this from NVIDIA: We have reviewed your NVIDIA GPU Grant Request and are happy support your work with the donation of (1) Titan Xp to support your research. Thanks! In case other people are interested, NVIDA’s GPU grant program provides ways for ...

### Thanks, NVIDIA

August 1, 2018 |

Andrew and I both received a note like this from NVIDIA: We have reviewed your NVIDIA GPU Grant Request and are happy support your work with the donation of (1) Titan Xp to support your research. Thanks! In case other people are interested, NVIDA’s GPU grant program provides ways for ... [Read more...]

### Thanks, NVIDIA

August 1, 2018 |

Andrew and I both received a note like this from NVIDIA: We have reviewed your NVIDIA GPU Grant Request and are happy support your work with the donation of (1) Titan Xp to support your research. Thanks! In case other people are interested, NVIDA’s GPU grant program provides ways for ... [Read more...]

### Where do I learn about log_sum_exp, log1p, lccdf, and other numerical analysis tricks?

July 12, 2018 |

Richard McElreath inquires: I was helping a colleague recently fix his MATLAB code by using log_sum_exp and log1m tricks. The natural question he had was, “where do you learn this stuff?” I checked Numerical Recipes, but the statistical parts are actually pretty thin (at least in my 1994 ... [Read more...]

### Where do I learn about log_sum_exp, log1p, lccdf, and other numerical analysis tricks?

July 12, 2018 |

Richard McElreath inquires: I was helping a colleague recently fix his MATLAB code by using log_sum_exp and log1m tricks. The natural question he had was, “where do you learn this stuff?” I checked Numerical Recipes, but the statistical parts are actually pretty thin (at least in my 1994 ... [Read more...]

### Where do I learn about log_sum_exp, log1p, lccdf, and other numerical analysis tricks?

July 12, 2018 |

Richard McElreath inquires: I was helping a colleague recently fix his MATLAB code by using log_sum_exp and log1m tricks. The natural question he had was, “where do you learn this stuff?” I checked Numerical Recipes, but the statistical parts are actually pretty thin (at least in my 1994 ... [Read more...]

### Three new domain-specific (embedded) languages with a Stan backend

January 9, 2018 |

One is an accident. Two is a coincidence. Three is a pattern. Perhaps it’s no coincidence that there are three new interfaces that use Stan’s C++ implementation of adaptive Hamiltonian Monte Carlo (currently an updated version of the no-U-turn sampler). ScalaStan embeds a Stan-like language in Scala. It’... [Read more...]
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