Greetings everyone, I am posting this question here since I cannot post it in the math and science learning materials section of the forum. My question is that sometimes in physics I get into a lot of involved math particularly linear algebra, Hilbert space, partial differential equations and complex analysis I want to brush up my skills in these areas by self studying a mathematical methods book. Do you have any recommendations for these kind of books? I currently own "Mathematical Methods for Students of Physics and Related Fields" by Hassani and a calculus and a linear algebra book. However sometimes these books are not sufficient and I need one which includes a detailed derivation of the properties of spherical harmonics and stuff related to group theory in quantum mechanics for example. After some search I found that the book by Hassani has a sequel named "Mathematical Physics: a Modern Introduction to its Foundations", there is a short book by Susan Lea named "Mathematics for Physicists" and yet another book "A Course in Modern Mathematical Physics: Groups, Hilbert Space and Differential Geometry" by Peter Szekeres. Actually some of these books lack some topics that the others have in them, that is what makes me confused. I would be happy to hear your opinions on this topic because I need to see the proof of every claim that a book makes.