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Alexa Louise Amundson - Notebook Transcription
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- 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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