This function feeds a high-amplitude sine function through a logit, offsetting so as to have the pulse start and stop at arbitrary times. It has an integral of one per period for large \(L\).
\[f(t) = \frac{c}{a - b} \frac{1}{1 + e^{L \left(sin(2\pi((t-a)/c + \xi)) - sin(2\pi\xi)\right)} }\]
where
\[\begin{aligned} t &= \text{time} \\ a &= \text{time at start of pulse} \\ b &= \text{time at end of pulse} \\ c &= \text{period length} \\ a &< b < c \\ L &= \text{an arbitrarily large number} \\ \xi &= \frac{3}{4} - \frac{b - a}{2c} \\ \end{aligned}\]

Last Friday at the Davis R Users’ Group, Mallory Johnson gave a presentation on RQDA, an R-based GUI tool for doing coding on documents for use in qualitative text analysis. Here’s the video, and you can view the slides here.

*[Sorry about reverb in the video]*

Last Friday at the Davis R Users’ Group, Grace Charles gave a presentation on structural equation modeling in R using the **Lavaan** package. Here’s the video and her slides. We’ve also posted Grace’s script from the presentation as a gist here. More resources that Grace mentioned in her talk below.

Last Fr Davis R Users’ Group, Jaime Ashander gave a presentation on and visualizing and diagnosing (G)LMMs in R. Here’s the video:
Jaime also wrote up the notes from his talk, including all the code, on his blog here (with the raw R Markdown file on github here). The material in the blog post is expanded and improved upon from the original talk, though this means the video and posted code don’t match exactly.

Today at the Davis R Users’ Group, Michael Koontz gave *tour de force* lesson in using R’s base graphics capabilities to plot data. Here’s the video:

Get Michael’s excellent annotated script, which covers much more than we got to during our tutorial, here.