Hello, I'm a recent graduate in Physics that's aiming for grad school. Quantum Mechanics was a course that destroyed me in undergrad. My department gave us a Differential Equations/Linear Algebra hybrid course that was a clusterf*ck, and our advanced Math for Science/Engineering class was also a clusterf*ck. I know that we need Linear Algebra and Differential Equations to understand QM, but I cannot quite find to what particular resource to go to understand more about why we use Hilbert Spaces. It sounds like I'll need some pure mathematics resource (which I don't mind), but what type of math course would dedicate to this material?