Would anyone here know where I could find some kind of tutorial that goes step by step of how to evaluate functional derivatives? I'm looking over my notes, trying to make sense of this functional derivatives stuff the teacher did in class, and it makes no sense at all. I'm not even in the realm of beginning to understand what's going on. There's dx's and deltas and partial derivative symbols flying around all over the place like some kind of mathematical Jackson Pollock painting. This was never covered in any math class I've had, the physics teacher just starts throwing it in and quickly going over all these strange manipulations you can do with it, like it's second-nature to us or something. And this is something I can't seem to find anything about online. Usually I can find tutorials on youtube or something, but nothing I type in regarding this stuff brings up any relevant results that I can understand.