From 7115e3ce7ae56ebff0fc7dae73327089f20c5dc0 Mon Sep 17 00:00:00 2001 From: raj_mathe Date: Thu, 15 Dec 2022 07:14:02 +0100 Subject: [PATCH] master > master: notebook - wk10 --- notebooks/week-10.ipynb | 236 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 236 insertions(+) create mode 100644 notebooks/week-10.ipynb diff --git a/notebooks/week-10.ipynb b/notebooks/week-10.ipynb new file mode 100644 index 0000000..825f8c5 --- /dev/null +++ b/notebooks/week-10.ipynb @@ -0,0 +1,236 @@ +{ + "cells": [ + { + "attachments": {}, + "cell_type": "markdown", + "metadata": {}, + "source": [ + "# Woche 10 #\n", + "\n", + "Diese Wochen beschäftigen wir uns mit Matrizen und Vektoren.\n", + "In diesem Notebook rechnen wir ein paar (Teil)aufgaben aus dem ÜB." + ] + }, + { + "cell_type": "code", + "execution_count": null, + "metadata": {}, + "outputs": [], + "source": [ + "'''IMPORTS'''\n", + "import os;\n", + "import sys; \n", + "\n", + "# NOTE: need this to force jupyter to reload imports:\n", + "for key in list(sys.modules.keys()):\n", + " if key.startswith('src.'):\n", + " del sys.modules[key];\n", + "\n", + "os.chdir(os.path.dirname(_dh[0]));\n", + "sys.path.insert(0, os.getcwd());\n", + "\n", + "from src.thirdparty.maths import *;\n", + "from src.thirdparty.misc import *;\n", + "from src.thirdparty.render import *;\n", + "from src.maths.diagrams import *;\n", + "\n", + "np.random.seed(8007253); # zur Wiederholbarkeit" + ] + }, + { + "cell_type": "code", + "execution_count": null, + "metadata": {}, + "outputs": [], + "source": [ + "'''BEISPIEL-SIGNAL'''\n", + "n = 100;\n", + "u = np.zeros((n,), dtype=complex);\n", + "u[8] = -0.7\n", + "u[58] = 1j * sqrt(2);\n", + "\n", + "display_signal(u, 'Beispiel eines Vektors als Signal dargestellt');" + ] + }, + { + "cell_type": "code", + "execution_count": null, + "metadata": {}, + "outputs": [], + "source": [ + "'''SEMINARAUFGABE 10.4 a)'''\n", + "n = 3;\n", + "t = linspace(0, n-1, n);\n", + "i, j = np.meshgrid(t, t);\n", + "theta = 2*pi * i * j / n;\n", + "\n", + "# definiere die Matrix F_n + die Vektoren u_nk\n", + "F_n = (1/sqrt(n)) * exp(-1j * theta);\n", + "u_n = [ (1/sqrt(n)) * exp(1j * theta[:, k]) for k in range(n) ];\n", + "\n", + "print(dedent(\n", + " f'''\n", + " Matrix:\n", + "\n", + " F_{n} = \\n{np.round(F_n, 3)}\n", + " '''\n", + "));\n", + "print('');\n", + "\n", + "# NOTE: Programmiersprachen können nicht exakt berechnen.\n", + "# Darum entstehen winzige Fehler, die sich durch Runden entfernen lassen.\n", + "print('Matrix-Vektor-Produkte:');\n", + "for k in range(n):\n", + " result = F_n @ u_n[k];\n", + " print(dedent(\n", + " f'''\n", + "\n", + " u_{{n {k}}} = {np.round(u_n[k], 3)}\n", + " F_n · u_{{n {k}}} = {np.round(result, 3)}\n", + " '''\n", + " ));" + ] + }, + { + "attachments": {}, + "cell_type": "markdown", + "metadata": {}, + "source": [ + "## Seminaraufgabe 10.4 b) ##\n", + "\n", + "Für $i\\in\\{0,1,\\ldots,n-1\\}$ ist die $i$-te von $\\mathcal{F}_{n}\\,u_{n,k}$\n", + "\n", + "$$\n", + " (\\mathcal{F}_{n}\\,u_{n,k})_{i}\n", + " = \\sum_{j=0}^{n-1}\n", + " (\\mathcal{F}_{n})_{ij}\\,(u_{n,k})_{j}\n", + " = \\sum_{j=0}^{n-1}\n", + " \\tfrac{1}{\\sqrt{n}}\n", + " \\exp(-\\imath\\tfrac{2\\pi\\,ij}{n})\n", + " \\cdot\n", + " \\tfrac{1}{\\sqrt{n}}\n", + " \\exp(\\imath\\tfrac{2\\pi\\,kj}{n})\n", + " = \\frac{1}{n}\\sum_{j=0}^{n-1}\n", + " \\underbrace{\n", + " \\exp(\\imath\\tfrac{2\\pi\\,(k-i)j}{n})\n", + " }_{= r^{j}}\n", + "$$\n", + "\n", + "wobei $r \\colonequals \\exp(\\imath\\tfrac{2\\pi\\,(k-i)}{n})$.\n", + "Wir haben, dass\n", + " $r = 1$\n", + " $\\Leftrightarrow$\n", + " $\\tfrac{k-i}{n} \\in \\Z$\n", + " $\\Leftrightarrow$\n", + " $i = k$,\n", + "da $0\\leq i,k \\leq n-1$.\n", + "
\n", + "Es gilt außerdem $r^{n} = \\exp(\\imath 2\\pi\\,(k-i)) = 1$.\n", + "
\n", + "Aus der o.s. Berechnung erhält man also\n", + "\n", + "$$\n", + " (\\mathcal{F}_{n}\\,u_{n,k})_{i}\n", + " = \\tfrac{1}{n}\\displaystyle\\sum_{j=0}^{n-1}r^{j}\n", + " = \\tfrac{1}{n}\n", + " \\begin{cases}\n", + " \\displaystyle\\sum_{j=0}^{n-1}1 &: &i = k\\\\\n", + " \\frac{1 - r^{n}}{1 - r} &: &\\text{sonst}\\\\\n", + " \\end{cases}\n", + " = \\tfrac{1}{n}\n", + " \\begin{cases}\n", + " n &: &i = k\\\\\n", + " \\frac{1 - 1}{1 - r} &: &\\text{sonst}\\\\\n", + " \\end{cases}\n", + " = \\delta_{ik}.\n", + "$$\n", + "\n", + "Darum $\n", + " \\mathcal{F}_{n}\\,u_{n,k}\n", + " = \\left(\\begin{matrix}\n", + " 0\\\\\n", + " 0\\\\\n", + " \\vdots\\\\\n", + " 1\\\\\n", + " \\vdots\\\\\n", + " 0\\\\\n", + " \\end{matrix}\\right)\n", + " \\begin{matrix}\n", + " \\\\\n", + " \\\\\n", + " \\\\\n", + " \\leftarrow k\\\\\n", + " \\\\\n", + " \\\\\n", + " \\end{matrix}\n", + " = \\mathbf{e}_{k}\n", + "$.\n" + ] + }, + { + "cell_type": "code", + "execution_count": null, + "metadata": {}, + "outputs": [], + "source": [ + "'''SEMINARAUFGABE 10.4 d)'''\n", + "n = 4;\n", + "t = linspace(0, n-1, n);\n", + "i, j = np.meshgrid(t, t);\n", + "theta = 2*pi * i * j / n;\n", + "\n", + "# definiere die Matrix F_n + die Vektoren u_nk\n", + "F_n = (1/sqrt(n)) * exp(-1j * theta);\n", + "u_n = [ (1/sqrt(n)) * exp(1j * theta[:, k]) for k in range(n) ];\n", + "\n", + "# Eingabe des Vektors:\n", + "F_mal_u = np.asarray([100, -3, 0, -3]); # = F_n @ u\n", + "\n", + "'''\n", + "NOTE: Folgende Koeffizienten wurden falsch erraten.\n", + "TODO: Wie lauten die richtigen Werte? -> Aufgabe!\n", + "'''\n", + "c = [10,10,40,50];\n", + "\n", + "# Aufschreibung des Signals »bzgl. der harmonischen Basis«:\n", + "# u = c[0]u_n[0] + c[1]u_n[1] + c[2]u_n[2] + c[3]u_n[3]\n", + "u_guess = sum([ c[k] * u_n[k] for k in range(n) ]);\n", + "\n", + "# Anzeige der Lösung:\n", + "display_signal(u_guess, 'Geschätztes Signal');\n", + "\n", + "# Verifikation von Lösung:\n", + "print(dedent(\n", + " f'''\n", + " %error := ‖u_guess – u‖ / ‖u‖\n", + " = ‖F_n · (u_guess – u)‖ / ‖F_n · u‖\n", + " ... wieso?? [Stichwort: unitär]\n", + " = ‖F_n · u_guess – F_n · u‖ / ‖F_n · u‖\n", + " = {linalg.norm(F_n @ u_guess - F_mal_u)/linalg.norm(F_mal_u):.2%}\n", + " '''\n", + "));\n" + ] + } + ], + "metadata": { + "kernelspec": { + "display_name": "Python 3", + "language": "python", + "name": "python3" + }, + "language_info": { + "codemirror_mode": { + "name": "ipython", + "version": 3 + }, + "file_extension": ".py", + "mimetype": "text/x-python", + "name": "python", + "nbconvert_exporter": "python", + "pygments_lexer": "ipython3", + "version": "3.10.8" + } + }, + "nbformat": 4, + "nbformat_minor": 2 +}