Whenever I see scientific code without units I scream inside my heart.
Everytime you write simulations of physical phenomena
(often using numpy or matlab), make sure to always have variables where the units are clear, e.g. :
lambda_m = 633e-9 #wavelentgh in meters
c_mps = 3e8 #speed of light in meters per seconds
freq_Hz = c_mps/lambda_m
Failure to keep good track of the units has led to disasters. Yet complete lack of clarity happens more often than not – just look at the code of a random scientist on github to witness the extent of the damage.
The reason why I am adamant about this is because a lot of time is wasted trying to debug code where it there’s a silly unit mismatch, and because we are doing physics.
Math versus physics
Why is coding without units such a terrible practice? It all boils down to the fact that computing is mostly about math and logic, and therefore not geared towards physical quantities. There is beauty in mathematical abstraction, but sometimes it doesn’t mean anything.
Take a mathematical statement that should be true:
Now ask yourself: what does it mean? If I add one orange to one apple:
1 orange + 1 apple = ?
It might sound silly but it’s actually pretty deep. You cannot add quantities which are not congruent. Yes, you may say that by adding one fruit with another fruit you get two fruits, but you’re cheating then.
This is somehow why object-oriented programming was invented
: with the notion of “classes”, you can add entities which are compatible, through the game of function overloading and other niceties. In an ideal world, physical quantities in simulations should all have their own class, where the units would be defined. Continue reading