I’ve been working on some code using GSL and wondering why it didn’t match the results I was getting from Mathematica and other programs. Well, one (of perhaps many) differences is that GSL defines the sinc function as
for \(x\neq 0\), but Mathematica defines it as
The latter is the definition I was using in my math, and I didn’t realize it didn’t match the one in GSL until I broke the code down to individual mathematical terms.
So remember to make sure that any code you use is actually doing what you think it’s doing!