# @stem_antics on Instagram

- **Type:** Video
- **Original URL:** https://www.instagram.com/p/Dcb9nHhSGux
- **Gondola URL:** https://gondola.cc/posts/69727805-stem-antics-instagram
- **Thumbnail:** https://img.gondola.cc/tr:w-,h-,fo-auto/postThumbnails/05f0c75072.jpg
- **Posted:** 2026-08-24T20:53:48.000+00:00
- **Account Owner:** Stem Antics (@stem_antics) — https://gondola.cc/stem_antics

## Caption

Every other logistics network on earth gets to say no. The USPS does not.

Universal service obligation means one price to move a letter, whether it crosses the street or reaches a cabin in the Brooks Range. No distance pricing, no refusing an address, no quietly dropping unprofitable routes. That single constraint removes the lever every commercial carrier pulls to keep its network tractable.

The numbers set the floor: 170.4 million delivery points in FY2025, growing by roughly a million a year while volume slides from its 2006 peak of 213 billion pieces. Fewer items, more doors, rising cost per stop even when nothing else changes.

Then the routing. A letter carrier is not solving the travelling salesman problem, because they are not visiting nodes, they are traversing edges. Every street segment on a route must be covered regardless of whether mail exists for it. That is the Chinese Postman Problem, formalised by Mei-Ko Kwan in 1960, and on an undirected graph it is beautifully tractable: find the odd-degree vertices, pair them by minimum-weight matching, duplicate those paths, and an optimal circuit falls out in polynomial time.

Real streets are not undirected. One-way roads, divided carriageways, park-and-loop segments walked in both directions, cul-de-sacs entered and exited on the same edge. That produces a mixed graph, and the mixed Chinese Postman Problem is NP-hard. Every route in America is an approximation.

Sorting is its own quiet miracle. Delivery Point Sequencing takes a tray of mail in arbitrary order and returns it in exact walk sequence using only two machine passes, a radix sort executed in steel, keyed off the eleven-digit routing code buried in the Intelligent Mail barcode’s 65 four-state bars.

Complexity is rarely about what a system does. It is about what it is forbidden to refuse.

#stemantics #logistics #operationsresearch #graphtheory #systemsengineering

## Stats

- **Views:** 5,099
- **Likes:** 96
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## Tags

systemsengineering, graphtheory, logistics, stemantics, operationsresearch

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