• 1 Post
  • 202 Comments
Joined 1 year ago
cake
Cake day: July 2nd, 2023

help-circle












  • affiliate@lemmy.worldtoScience Memes@mander.xyzSo much
    link
    fedilink
    English
    arrow-up
    3
    ·
    8 days ago

    that would be a lot clearer. i’ve just been burned in the past by notation in analysis.

    my two most painful memories are:

    • in the (baby) rudin textbook, he uses f(x+) to denote the limit of _f _from the right, and f(x-) to denote the limit of f from the left.
    • in friedman analysis textbook, he writes the direct sum of vector spaces as M + N instead of using the standard notation M ⊕ N. to make matters worse, he uses M ⊕ N to mean M is orthogonal to N.

    there’s the usual “null spaces” instead of “kernel” nonsense. ive also seen lots of analysis books use the → symbol to define functions when they really should have been using the ↦ symbol.

    at this point, i wouldn’t put anything past them.




  • affiliate@lemmy.worldtoScience Memes@mander.xyzSo much
    link
    fedilink
    English
    arrow-up
    4
    ·
    8 days ago

    unless f(x0 ± δ) is some kind of funky shorthand for the set f(x) : x ∈ ℝ, x - x0 | < δ . in that case, the definition would be “correct”.

    it’s much more likely that it’s a typo, but analysts have been known to cook up some pretty bizarre notation from time to time, so it’s not totally out of the question.



  • affiliate@lemmy.worldtoScience Memes@mander.xyzSo much
    link
    fedilink
    English
    arrow-up
    2
    arrow-down
    1
    ·
    9 days ago

    i think the ε-δ approach leads to way more cumbersome and long proofs, and it leads to a good amount of separation between the “idea being proved” and the proof itself.

    it’s especially rough when you’re chasing around multiple “limit variables” that depend on different things. i still have flashbacks to my second measure theory course where we would spend an entire two hour lecture on one theorem, chasing around ε and η throughout different parts of the proof.

    best to nip it in the bud id say


  • affiliate@lemmy.worldtoScience Memes@mander.xyzSo much
    link
    fedilink
    English
    arrow-up
    5
    arrow-down
    2
    ·
    9 days ago

    i still feel like this whole ε-δ thing could have been avoided if we had just put more effort into the “infinitesimals” approach, which is a bit more intuitive anyways.

    but on the other hand, you need a lot of heavy tools to make infinitesimals work in a rigorous setting, and shortcuts can be nice sometimes