I have a long-term client who needs to schedule doctors according to their capabilities, but also according to a complex set of rules. I developed a working solver years ago using OR-Tools and CP-SAT. Everytime they ask for some small improvement, I take the opportunity to revisit my core abstractions to see if I can’t figure out a more elegant way to approach the problem. Recently I’ve been studying a published example of nurse rostering that uses the add_automaton() function from CP-SAT. I believe this is a good approach that will fix all the things, so I am writing this series of blog posts. In the end, I think I’ve unvented something relating to the DFA graph’s dual, but we’ll see if that has legs.

Recently I have been working on better debugging of CP-SAT models. In order to test the various functions, I wanted to load a saved model and find variables and constraints. It turns out, I haven’t ever loaded a model from a pbtxt dump file. I searched in the forums and GitHub issues, and the best advice I found didn’t work. This short blog (Hello 2026!) is about how to load a CP-SAT model from a protobuf text dump in Python, as of version 9.16 of OR-Tools.

This post is mostly to try to get myself back in the habit of posting new blog content. I was looking over some of the examples in the OR-Tools repository, and I started playing around with the tasks and workers assignment problem. The original example can be found here: https://github.com/google/or-tools/blob/master/examples/python/tasks_and_workers_assignment_sat.py. In this post I go through the code bit by bit to understand what is going on, and then try some small changes to see what happens. I hope a newcomer to OR-Tools or CP-SAT might find this useful for starting their own exploration of the examples in the repository.

I was working through an example CP-SAT program on sports team scheduling, and I found a bit of AddBoolOr logic that I didn’t understand. So I wrote up a short program to explore what was going on.