# Posts

### The cost of evaluating an expression instead of using the language directly

In a recent blog post I used something like this (for use in a call to optim()): obj_fun_expr <- expression((x^4 + 4 * x^2 * y^2 - …

### Correlation is not transitive, in general at least: A simulation approach

Let $$\rho_{XY}$$ be the correlation between the stochastic variables $$X$$ and $$Y$$ and similarly for $$\rho_{XZ}$$ and …

### Automatic 'testthat' test skeletons with new R package 'roxytest' extending 'roxygen2'

It is important to test software. One approach is unit-testing, and for R packages this can e.g. be done using testthat. It is also …

### Correlation is not transitive, in general at least

Update Aug 10, 2019: I wrote a new blog post about the same as below but using a simulation approach. Update Aug 27, 2019: Minor change …

### How much pizza and how much frozen yogurt?

Update Aug 27, 2019: I wrote a new blog post showing that Ryacas can now solve the system of equations directly without using optim(). …

### Piano chords in R with the R package 'pichor'

I am learning how to play piano. In that process, I needed charts with piano chords. I know it is good practise to construct the chords …

### Major update of Ryacas (R Interface to the Yacas Computer Algebra System)

Update Aug 27, 2019: Minor change in how equations are solved (from version 0.9.0.9122). We (Søren Højsgaard and I) are preparing a new …