# Recycling old solutions

A few years ago I found myself in need of a simple program to make pixel art. At the time I had access to the PHP suite of graphical libraries, and the ability to manipulate the HTML DOM, so armed with these tools I put together a simple tool that would allow me to create small images online, which I called the Painter. It was not particularly efficient, but it got the job done, and did so for free. (Now that the HTML canvas is supported pretty much everywhere that tools needs to be rewritten for the latest generation of browser technology.) During the development of this tool I found myself wanting to solve the following problem: Given a two dimensional rectangular array of squares, how can I find all squares that reside within a given boundary? It’s a fairly straightforward problem, but one that requires keeping track of two lists of squares, and one that should scale, as far as possible, with $$n^2$$ or lower. After some head scratching and experimenting with a few lines of code I found the solution I needed, tweaked it a bit, and was fairly impressed with its elegance.

Then a few years later I was talking with my current boss and she said something along the lines of “You shouldn’t take on these extra projects, they take up your time and distract you.” It’s a fair point that with over 50 coding projects, and about a dozen more nebulous and time consuming projects, I have a lot on my plate, but on the other hand they serve some very useful purposes that I can’t get elsewhere. One of the most useful contributions they give is that they are often the first testing ground for solving problems. The lessons I learn in Javascript, PHP, and python are often directly applicable to my physics work.

A few months ago I found myself having to deal with the CMS Preshower system. I wanted to make a map of the system to that I could visualise how it looked in three dimensions. The only things I really knew as that it was arranged in a grid of square components (each square component subsequently arranged in strips) and that I had a tool where if I could access a single square I could access all of its neighbours. Since the physical extent of the preshower system gave me an obvious boundary I found myself with a very familiar sounding problem… Without even needing to look up the code from the Painter tool I wrote down the solution in a few lines and in about 10 minutes. What may have taken me a few hours of framing the question, determining how to find the solution, and subsequently implement it was reduced to a trivially solved problem with a minimal footprint of CPU time and memory. This later lead on to the development of the $$\eta-\phi$$ map, which is still under development and may eventually lead to more breakthroughs for the CMS experiment.

I make it a point to not invest much time in a project unless it’s going to teach me a new skill or show me how a new technology or feature works. By exploring what was possible with a few rudimentary tools I was able to unwittingly give myself the solution to a real world problem that saved a lot of headaches and time. Whether the extra projects are worth the extra time is a different discussion entirely (I personally think they are, and also think that what I learn in physics programming today I can use in private enterprise tomorrow) and one that deserves some serious thought. For now I am happy that I have a huge pool of experience to draw on that only keeps growing in time.