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@blackboxprogramming

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@blackboxprogramming

Alexa Louise Amundson - Notebook Transcription

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  1. Computer Science & Logic: The Halting Problem (Page 1)
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    Complex & Imaginary Numbers:
  • (a+ib)(a-ib) = a^2 - ibib
  • Imaginary: (y+x)^2 y
  • Real: Real (y+x)^2
  • Euler's formula expansion: e^(ix) = 1 + ix - x^2/2 - i(x^3)/6 + x^4/24...

Paradoxes & Abstraction:

  • Golden Braid: A reference to levels of abstraction and paradoxes.
  • "This sentence is false" -> refers to its own truth value.
  • Cantor diagonalization -> linked to the Halting problem.

The Halting Problem:
The notes map out a thought experiment for a hypothetical program, 'h', that predicts if another program will loop forever or halt.

  • Program 1 -> [h]: Input I into a potential program h.
  • h will tell you: will this problem halt? or will it not? (Because some problems will go on forever).
  • Examples:
    • x=4, while x > 3: x+=1 -> LOOPS FOREVER
    • x=4, while x < 1000: x+=1 -> Halts.
  • The Paradox (h+):
    • Take the source code (e.g., 11001011) and use that code as both the program and the input.
    • Feed x as data into itself (x = h+).
    • If h halts, h+ begins an infinite loop. If h loops, h+ halts.
    • Conclusion: "Does it loop or halt? It's a paradox! But h does not exist!"

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2. Number Theory: The Möbius Function

Definitions & Rules:

  • The Möbius function is a multiplicative number-theoretic function.
  • For any positive integer n, define \mu(n) as the sum of the primitive n-th roots of unity.
  • Factorization rules:
    • \mu(n) = 0 if n has one or more repeated prime factors
    • \mu(n) = 1 if n = 1
    • \mu(n) = (-1)^k if n is a product of k distinct primes
  • \mu(n) != 0 indicates that n is square-free.
  • First few values: 1, -1, -1, 0, -1, 1, -1, 0, 0, 1, -1, 0...

Formulas & Series:

  • Mertens Function (Summatory function of Möbius): M(x) = Sum_{n \le x} \mu(n)
  • Dirichlet Series (Multiplicative inverse of the Riemann zeta function): Sum_{n=1}^{\infty} \mu(n)/n^s = 1/\zeta(s) ; Re(s) > 1
  • Lambert Series: Sum_{n=1}^{\infty} (\mu(n)x^n)/(1-x^n) = x ; |x| < 1
  • Kronecker Delta Relation: It satisfies Sum_{d|n} \mu(d) = \delta_{n,1}
  • Infinite Sums:
    • Sum_{n=1}^{\infty} \mu(n)/n = 0
    • Sum_{n=1}^{\infty} (\mu(n) \ln(n))/n = -1
    • Sum_{n=1}^{\infty} \mu(n)/n^2 = 15/\pi^2

Historical Note: Gauss considered the Möbius function over 30 years before Möbius, proving that for a prime number p, the sum of its primitive roots is congruent to \mu(p - 1) (mod p).

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3. Probability & Math: Gaussian Functions & Fourier Transforms

Gaussian Basics:

  • Used to represent the probability density function of a normally distributed random variable.
  • Expected value \mu = b, Variance \sigma^2 = c^2.
  • Standard form: f(x) = (1 / (\sigma\sqrt{2\pi})) * e^(-(1/2)((x-\mu)/\sigma)^2)
  • Arbitrary constants: f(x) = a * e^(-(x-b)^2 / 2c^2) (where a is peak height, b is center position, c controls width).

Fourier Transform Proofs:

  • Transform of a Gaussian: F{a * e^(-bx^2)} = (a / \sqrt{2b}) * e^(-\omega^2 / 4b)
  • The notes map out the integration proof using substitution (t = x + i\omega/2b), showing that the Fourier transform of a Gaussian is also a Gaussian.
  • Derivative Properties:
    • Time domain: F{f'(x)} = i\omega F(\omega)
    • Frequency domain: F{x f(x)} = i * d/d\omega F(\omega)

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4. Physics: Quantum Mechanics & Energy

Schrödinger Equation & Operators:

  • Time-dependent equation: i\hbar (\partial/\partial t)\Psi = H\Psi
    • i = square root -1
    • \hbar = Planck's constant (reduced)
    • \Psi = quantum wave function
    • H = Hamiltonian operator
  • Harmonic Oscillator:
    • Classical Energy: (1/2)mv^2 + (1/2)kx^2 = E
    • Hamiltonian Operator transition: p => (\hbar/i)(\partial/\partial x)
    • Quantum Hamiltonian: H -> (-\hbar^2 / 2m)(\partial^2/\partial x^2) + (1/2)kx^2
    • Eigenvalue equation: H\Psi = E\Psi

Uncertainty & Photons:

  • Heisenberg Uncertainty Principle: \Delta p \Delta x \ge \hbar/4\pi
  • Energy of a photon: E = h\nu = hc/\lambda
  • Photoelectric effect: (1/2)mv_{max}^2 = eV_0 = hf - \phi

Fundamental Constants & Bohr Model:

  • r = (n^2 h^2 \epsilon_0) / (\pi m e^2) \propto h^2
  • v = e^2 / (2 \epsilon_0 n h) \propto 1/n
  • Fine-Structure Constant (\alpha): \alpha = (1 / 4\pi\epsilon_0) * (e^2 / \hbar c) \approx 1/137
  • Speed of light (c): 3 * 10^8 m/s
  • Elementary charge (e): 1.602 * 10^-19 C

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