How to quickly learn to read mathematical formulas "from a sheet"?

Question

Mathematics

While studying at the physics and mathematics school and institute, all the variety of symbols and syntax of mathematical formulas somehow did not stick in my head. There were integral sums, nothing more.
Now I'm reading someone's work on the topic I need, and as soon as I come across formulas, panic panic.
How to quickly figure it out? Maybe something on Coursera/Udacity?
From the fails for a couple of days: what are the double vertical lines and 2-under-2?

Or here's a "very clear" definition :

• sup - what is this function?
  
• double vertical bars is it a module or something else?
  
• P - not familiar to me record ..
  

Probably, these records were conceived as a convenient and universal way of recording that everyone understands, but for me this is some kind of unfamiliar programming language. You can, of course, look for answers in each specific case. Find out that double vertical is the length of the vector, and P is the product. But maybe there is some kind of crash-course where they give an easy-to-understand overview of the whole variety of records?

Answer 1

I found an excellent cheat sheet that solves all my questions: an appendix to Sebastian Raschka's book "Introduction to Artificial Neural Networks and Deep Learning: A Practical Guide with Applications in Python"
sebastianraschka.com...appendix_a_math_notation.pdf
Notebook books on github: rasbt/deep -learning-book

Answer 2

||x|| this is the norm x.
2-under-2 is, in theory, indexes, why are they here - xs.
P is like a sum, only the product
sup is the supremum
. Take a matan textbook, it happens there at the beginning. Ilyin, Sadovnichy, Sendov.

Answer 3

In order to be able to read such formulas, you need to have a good idea of ​​what kind of objects and operations they are, the classic trio of subjects will help you with this: mathematical analysis, linear algebra, discrete mathematics (including discrete probability theory).