## 2020

### Convenient sentinels for keyword arguments in Julia

When writing a high-level interface function that takes many keyword options, the desired default values may sometimes be best set conditionally based on the values of other keywords. In such a case, handling the interdependency among keywords can be easiest if the function declaration uses a sentinel value like

`nothing`

, but then the type restrictions must be rewritten to`Union{T, Nothing}`

in every case, which can get tedious. With a relatively simple macro, though, we can automate this transformation.### Pre-normalizing Legendre Polynomials Addendum

The main

`Legendre.jl`

series contains a detailed article considering the numerical accuracy of the recurrence implementation as a whole. This short addendum presents a mathematical transformation which is used to improve the accuracy of one of the recurrence relation coefficients for the spherical harmonic normalization.### Plots of the Spherical Harmonics Eigenmodes

This posting is a simple addendum to the much longer article, Notes on Calculating the Spherical Harmonics. Because it had already grown so long, I left out making any plots of individual eigenmodes, so here I simply present plots of the first 50 degrees of the pure spherical harmonic eigenmodes, which can be useful to help visualize some of the symmetry properties that were discussed in the longer article.

### Typesetting ADS references in BibLaTeX bibliographies

The NASA Astrophysical Data System (ADS) is a database of pre-print and peer-reviewed papers spanning physics and astronomy. In particular, the ADS entry links together the pre-print and peer-reviewed papers, so including the ADS entry in a printed BibLaTeX bibliography can be a big convenience to readers of your paper.