Keeping with my pattern of posts based on OR Tools GitHub issues, (issue #968) asked how to model having multiple alternatives for pickup locations and dropoff locations.

A question was posed recently on the Google OR Tools GitHub issues (issue #922) that asked whether it was possible to set up FIFO or LIFO constraints. I’d never done that before, but it seemed straightforward to implement. There were a few wrinkles though, so I thought I’d write them up for my future self.

Generating random pickup and delivery pairs has been a pain point for me in the past. The problem comes with generating reasonable destination time windows. In my latest cycle of coding up a test environment for pickup and delivery problems with time windows (PDPTW), I had an insight that both makes generating random deliveries easier, and also improves the actual solution process of the PDPTW problem.

We’ve recently been doing a lot of work with Google’s OR Tools. One of our clients discovered a surprising result while setting disjunctions. As expected, with no disjunctions, all nodes are required. But if you set just one disjunction, most nodes are dropped. We didn’t have a good answer for what was going on, so I decided to explore the situation in this post.

Grace came home last weekend for her fall break, and we had some great discussions about the state of the world. On the drive to our favorite place to eat the girls started talking about the recent IPCC report on keeping the world at or below a 1.5°C rise in temperature from pre-industrial levels.

Google’s OR Tools is incredibly useful, but can be tricky to use. I subscribe to the mailing list to keep up on other users’ questions and solutions, and usually I just read and learn. But yesterday a question popped up on the OR-Tools mailing list that I could answer: how to force some node to occur before another node.

This is the first post on our new blog. Over the past two weeks, I (James) have re-done our website twice. First I migrated from a custom node.js site to Jekyll, and then from Jekyll to Hugo.