Recent content by Office_Shredder

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    I Question about vector spaces and subsets

    Counterpoint: ##\mathbb{Q}\subset \mathbb{R}##, is a 1 dimensional vector space over itself but it's not a subspace of the one dimensional real vector space ##\mathbb{R}##. I would argue the addition is the same :)
  2. O

    I How to implement proper error estimation using MC

    You can kind of just compute this exactly. For any possible choice of x, you know what fraction of the time your sampling will return a 0 instead of a 1. Then you can compute things like what value of x makes it so you would only see at least as extreme a result as you got 5% of the time (in...
  3. O

    I How to implement proper error estimation using MC

    Are y and the standard deviation of dy exactly known to you?
  4. O

    I A step in a proof of linear dependence of ODE solutions

    I think the point is that for any fixed x the functions are just numbers.
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    I Riemann integrability and uniform convergence

    I suspect it's a typo and the 3 in the denominator is supposed to be gone. Edit: actually I take it back. Let's say ##M_k>N_k##. Then where ##M_k## is realized, ##f_N## is within ##\epsilon/(3(b-a))## of ##M_k## and is guaranteed to not be larger than ##N_k##, showing the inequality in your...
  6. O

    I How to manipulate functions that are not explicitly given?

    The first function in the original post, that would probably refer to the third variable actually
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    I How to manipulate functions that are not explicitly given?

    The Landau case, ##\frac{\partial L}{\partial v^2}## is the same thing, you could let ##x_1=v^2## and you're just doing the chain rule. ##\frac{\partial L}{\partial v^2}=\frac{\partial L}{\partial x_1}## the ##v^2## in the denominator is the author's way of just making sure you don't compute...
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    I How to manipulate functions that are not explicitly given?

    Yeah, this is very abused notation. I think it helps to separate the variables a bit. Let ##f=f(x_1)##, and let ##x_1=y+\alpha \eta##. Then it's really ##\frac{\partial f}{\partial x_1}\frac{\partial x_1}{\partial \alpha}##. Unfortunately people don't want to need 2n variables for an n...
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    I How to manipulate functions that are not explicitly given?

    The simple example you are looking at is just the chain rule. ##\frac{\partial f}{\partial \alpha} =\frac{\partial f}{\partial y}\frac{\partial y}{\partial \alpha}## (where in this case the partial derivatives are full derivatives)
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    Relationship between autonomous system and related single equation

    I think the simplest thing to consider is just like, consider the curve sketched out by##(t,t^2)## compared to ##(t^3,t^6)##. Both of them traverse the parabola ##y-x^2=0## but the behavior of a particle traveling according to each of the two functions of t is pretty different. For example...
  11. O

    What would you memorize if you could?

    It's just a list of names of textbooks, technically by the way the request was worded
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    A Axiom of choice: Replacing a strong condition with a weaker condition

    If you subtract ##A\cap C## from the left side of everything, and ##B\cap D## on the right side, then you have reduced to the case of no intersection as long as you can show the following result: If ##B\subset A##, ##D\subset C##, ##D\approx B##, ##A\approx C##, then ##A-B \approx C- D##
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    I Normal Mode calculation steps

    A and B are matrices you know, and ##\,omega## is a number that you know, so you can plug them all in and you get like like ##Cx=0## for some matrix ##C## that you know. You might at first guess that gives you two equations and two unknown (##x## is a vector of 2 dimensions, the 0 on the right...
  14. O

    Non-Differentiable Function proof

    I find it a bit weird to suggest someone compute the derivative of cos(x) as a substep in their struggle to compute the derivative of cos(x). I don't think the suggestion is really that appropriate - either we know the derivative of cos(x) is sin(x) and we should use that fact directly, or we...
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    I About the definition of vector space of infinite dimension

    I think if a Hilbert space has a countable Schauder basis, then it has a countable Hilbert basis. You can basically just apply Grahm Schmidt on the Schauder basis and you get a set with the same span, and everything is orthonormal. I suspect the same is true (cardinality of Schauder and...
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