ELI5: Explain Like I'm 5

Lagrangian relaxation

Lagrangian relaxation is like playing a game where you have to follow a bunch of rules, but some of the rules are really difficult to follow at the same time. So instead of trying to do everything perfectly, you focus on the most important rules and give yourself a little bit of wiggle room on the others.

Imagine you have to build a tower out of blocks, but you can only use a certain number of blocks and they all have to fit together perfectly. That's a lot of rules to follow! But maybe the most important rule is that your tower can't fall over. So you focus on making sure your tower is steady and ignore the other rules for a little bit - maybe you use some blocks that aren't the perfect size, or you leave a gap here and there.

Now imagine you're trying to solve a really complicated puzzle where you have to find the best way to do a bunch of things. Like maybe you're planning a road trip and you want to find the fastest route, but you also want to see some cool stuff along the way. There are a lot of rules you have to follow - like you can't drive off the road, and you have to stay within your budget, and you have to be back in time for work.

Lagrangian relaxation helps you solve this puzzle by focusing on the most important rules first - like getting to your destination on time. Then you give yourself some wiggle room on the other rules - like maybe you take a slightly longer route if it means you get to see something cool. At the end, you have a good solution that isn't perfect, but it's the best you can do while still following the most important rules.

So basically, Lagrangian relaxation is a way to solve complicated problems by focusing on the most important parts and giving yourself some flexibility on the rest. It's like building a tower out of blocks, or planning a road trip - you can't do everything perfectly, but you can do the most important things really well and still have a good outcome.