Mark A. Wolters

Package **scdensity** unifies a few methods for enforcing shape constraints on probability density estimates. Because it uses the familiar kernel density estimator, getting shape-constrained estimates should be no more difficult than getting regular estimates.

Shape constraints are especially useful if you have a small data set or the data is noisy. For example, the `chickwts`

data set in R gives the weights of chicks that were fed with different diets. The `sunflower`

and `soybean`

groups have 12 and 14 observations, respectively. The figures below show what you get with a standard kernel density estimator (KDE) versus a shape-constrained KDE. The shape constraint used here was the `twoInflections+`

constraint in `scdensity`

. It ensures that the estimate has only two inflection points, and its derivative has only three inflection points. The constraint makes the nonparametric estimate look more like a parametric one. Which option would you rather use to communicate your results?

The *ffslides* (“freeform slides”) LaTeX class started as a bunch of macros I wrote to allow me to create presentations using the article class. But as I have ended up using them exclusively to produce my presentations and even certain research notes for my own use, I thought it might be worthwhile to work it up into a document class. The class might be for you if:

- You want to design slides in your own style.
- You want to be able to place some text or a figure anywhere on a slide, without having to fight some automatic class behaviour.
- You want to avoid everyone knowing instantly that you used beamer to make your slides.

If you’re interested, you can view the CTAN page, or you could download the manual (which is itself made using the class) to see what it’s about.

I have written a small R package called **kofnGA**. It implements a genetic algorithm to do subset selection. It’s for picking subsets of a fixed size k from n alternatives. The main selling point of the package is that it works with an objective function that is arbitrary and user-defined. So it should be worth a shot for any subset selection problem you happen to have. A paper demonstrating and evaluating the package is available in Journal of Statistical Software.

(If you’re curious about the little badge above with the download stats, see here)

There is sample code to accompany a chapter written by me and Charmaine Dean in the book **Current Air Quality Issues**. See the page.

If you use XYplorer file manager, you may wish to run Windows Search inside the program. I’ve written a script to do this.

My contributions to MATLAB central file exchange. Most useful here is a small function to make a nice dotplot.

The autologistic regression model demo on this website is an example of using javascript/html/css to build an interactive numerical demonstration and visualization.