SHARP lib not found

I am trying to install the program as described. However, when executing cmake, I get an error:

`SHARP lib not found. Set SHARP_DIR to find it.`

I've tried to export the variable to the absolute path of sharp-nsls2 on my machine. That doesn't work, though. How can I proceed?

(Ubuntu 18.04 LTS, all other dependencies are fulfilled as far as I can see.)