# install GSL with homebrew on Mac:
brew install gsl

# install GSL on Linux:
sudo apt-get install libgsl-dev

# on Linux, if the ggraph dependency fails, run:
sudo apt install libfontconfig1-dev
# which appears to fix a sysfonts issue. We're not sure why this is necessary.

# on Windows, we suggest installing RTools (which includes a distribution of GSL):
https://cran.r-project.org/bin/windows/Rtools/