How to learn functional analysis

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Discussion Overview

The discussion revolves around the prerequisites for learning functional analysis, particularly the necessity of understanding topology beforehand. Participants share their experiences and recommendations regarding textbooks and study approaches in the context of self-learning functional analysis.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant expresses uncertainty about the need to study topology before functional analysis, citing difficulty and time constraints.
  • Another participant argues that topology is not strictly necessary for functional analysis, although it may be beneficial, and recommends Kreyszig's book as a suitable starting point.
  • Concerns are raised about whether Kreyszig's book covers all necessary material for a functional analysis course, with one participant affirming that it does cover the basics expected in an introductory class.
  • Another participant suggests that learning point-set topology could be worthwhile, noting that it may be easier than functional analysis if approached with the right textbook.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether topology is essential before studying functional analysis. There are competing views on the necessity and difficulty of topology in relation to functional analysis.

Contextual Notes

Some participants mention the limitations of certain textbooks, indicating that while Kreyszig's book is accessible, it may not delve into all topics comprehensively. There is also mention of varying levels of difficulty associated with different textbooks.

wdjhit
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I major in physics, but I'm also very interested in mathematics, especially analysis. Until now, I have taken mathematical analysis and real analysis. Now, I want to learn functional analysis by myself,
and my teacher adviced me to read topology first. But I found it difficult to understand and may take too much time. So, do I really need to know topology before I study functional analysis? Can you give me some advice?
 
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wdjhit said:
I major in physics, but I'm also very interested in mathematics, especially analysis. Until now, I have taken mathematical analysis and real analysis. Now, I want to learn functional analysis by myself,
and my teacher adviced me to read topology first. But I found it difficult to understand and may take too much time. So, do I really need to know topology before I study functional analysis? Can you give me some advice?

No! You don't need to know topology for functional analysis (although it cerainly helps). A very good book that introduces functional analysis at a rather basic level (meaning: no prereq knowledge of topology and measure theory) is Kreyszig: https://www.amazon.com/dp/0471504599/?tag=pfamazon01-20 The book goes rather far without assuming too much. Of course, with only a basic prereq knowledge assumed, it can't do everything in the "best" possible way. For example, the ##L^2## spaces are not treated in the most intuitive way, since it requires measure theory.

Another good book is Reed & Simon: https://www.amazon.com/dp/0125850506/?tag=pfamazon01-20 However, it is rather terse, and I wouldn't recommend it to an undergrad without much experience in pure math. He doesn't assume topology and measure theory, but he goes over it far too quickly to be of any use to an undergrad. It's one of my favorite books though.

More advanced books definitely need a good and solid knowledge of topology and measure theory.

If you're interested in PDE, then this book is good: https://www.amazon.com/dp/0387709134/?tag=pfamazon01-20 Although it might be too advanced for an undergrad.

If you're interested in QM, then this book is excellent: https://www.amazon.com/dp/0486453278/?tag=pfamazon01-20 It only deals with Hilbert spaces though, and not with Banach spaces. But he does go a long way without many prereqs.
 
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Thanks very much! Actually I have the book written by Kreyszig. It is simple, and clear, and also because of this I'm worried whether the book can offer me all the materials that a functional class covers. Anyway, I can have a look at the other books you recommended and finally choose one for further studying. Many thanks!
 
wdjhit said:
Thanks very much! Actually I have the book written by Kreyszig. It is simple, and clear, and also because of this I'm worried whether the book can offer me all the materials that a functional class covers. Anyway, I can have a look at the other books you recommended and finally choose one for further studying. Many thanks!

Yes, it covers all that a first class on a topic covers. You can of course go way beyond this. It depedends on what your goal is and why you study it.
 
If you've taken real analysis, why not learn point-set topology anyways? It isn't difficult if you have the right textbook (i.e. don't start off with Willard!) and imo easier than functional analysis.
 

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