数学 - Python - JavaScript - 解析学 - 積分 - いくつかの計算練習 - (n!)^(1/n)の計算(階乗、累乗、極限)

学習環境

解析入門原書第3版 (S.ラング(著)、松坂和夫(翻訳)、片山孝次(翻訳)、岩波書店)の第3部(積分)、第12章(いくつかの計算練習)、1((n!)^(1/n)の計算)の問題1.を取り組んでみる。

1. $\begin{array}{l} \lim_{n \to \infty} {(\frac{(3 n)!}{n^{3 n}})}^{\frac{1}{n}} \\ = \lim_{n \to \infty} {(\frac{(3 n!)}{{(3 n)}^{3 n}} \cdot 3^{3 n})}^{\frac{1}{3 n} \cdot 3} \\ = \lim_{n \to \infty} {(\frac{(3 n)!}{{(3 n)}^{3 n}})}^{\frac{1}{3 n} \cdot 3} \cdot 3^{3} \\ = {(\frac{1}{e})}^{3} \cdot 27 \\ = \frac{27}{e^{3}} \end{array}$
2. $\begin{array}{l} \lim_{n \to \infty} {(\frac{n^{n}}{n!} \cdot \frac{1}{n^{n}} \cdot \frac{(3 n)!}{n^{2 n}})}^{\frac{1}{n}} \\ = \lim_{n \to \infty} {(\frac{n^{n}}{n!} \cdot \frac{(3 n)!}{n^{3 n}})}^{\frac{1}{n}} \\ = e \cdot \frac{27}{e^{3}} \\ = \frac{27}{e^{2}} \end{array}$

コード(Emacs)

Python 3

#!/usr/bin/env python3
from sympy import pprint, symbols, exp, factorial, oo, plot, floor

print('1.')

n = symbols('n', integer=True)
ts = [(factorial(3 * n) / n ** (3 * n)) ** (1 / n),
      (factorial(3 * n) / (factorial(n) * n ** (2 * n))) ** (1 / n)]

for i, t in enumerate(ts):
    print(f'({chr(ord("a") + i)})')
    pprint(t.limit(n, oo).doit())
    print()

入出力結果(Terminal, Jupyter(IPython))

$ ./sample1.py
1.
(a)
    -3
27⋅ℯ  

(b)
    -2
27⋅ℯ  

$

HTML5

<div id="graph0"></div>
<pre id="output0"></pre>
<label for="r0">r = </label>
<input id="r0" type="number" min="0" value="0.5">
<label for="dx">dx = </label>
<input id="dx" type="number" min="0" step="0.001" value="0.01">
<br>
<label for="x1">x1 = </label>
<input id="x1" type="number" value="1">
<label for="x2">x2 = </label>
<input id="x2" type="number" value="20">
<br>
<label for="y1">y1 = </label>
<input id="y1" type="number" value="0">
<label for="y2">y2 = </label>
<input id="y2" type="number" value="6">

<button id="draw0">draw</button>
<button id="clear0">clear</button>

<script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/d3/4.2.6/d3.min.js" integrity="sha256-5idA201uSwHAROtCops7codXJ0vja+6wbBrZdQ6ETQc=" crossorigin="anonymous"></script>

<script src="sample1.js"></script>

JavaScript

let div0 = document.querySelector('#graph0'),
    pre0 = document.querySelector('#output0'),
    width = 600,
    height = 600,
    padding = 50,
    btn0 = document.querySelector('#draw0'),
    btn1 = document.querySelector('#clear0'),
    input_r = document.querySelector('#r0'),
    input_dx = document.querySelector('#dx'),
    input_x1 = document.querySelector('#x1'),
    input_x2 = document.querySelector('#x2'),
    input_y1 = document.querySelector('#y1'),
    input_y2 = document.querySelector('#y2'),
    input_n0 = document.querySelector('#n0'),
    inputs = [input_r, input_dx, input_x1, input_x2, input_y1, input_y2],
    p = (x) => pre0.textContent += x + '\n';

let factorial = n => n < 1 ? 1 : n * factorial(n - 1),
    fns = [
        [x => {
            let n = Math.floor(x);
            
            return (factorial(3 * n) / n ** (3 * n)) ** (1 / n);
        }, 'red'],
        [x => {
            let n = Math.floor(x);

            return  (factorial(3 * n) / (factorial(n) * n ** (2 * n))) ** (1 / n);
        }, 'green']
    ];

let draw = () => {
    pre0.textContent = '';

    let r = parseFloat(input_r.value),
        dx = parseFloat(input_dx.value),
        x1 = parseFloat(input_x1.value),
        x2 = parseFloat(input_x2.value),
        y1 = parseFloat(input_y1.value),
        y2 = parseFloat(input_y2.value);

    if (r === 0 || dx === 0 || x1 > x2 || y1 > y2) {
        return;
    }    
    
    let points = [],
        lines = [[x1, 27 / Math.exp(3), x2, 27 / Math.exp(3), 'blue'],
                 [x1, 27 / Math.exp(2), x2, 27 / Math.exp(2), 'orange']];
    
    fns
        .forEach((o) => {
            let [f, color] = o;
            for (let x = x1; x <= x2; x += dx) {
                let y = f(x);

                points.push([x, y, color]);
            }
        });
    
    let xscale = d3.scaleLinear()
        .domain([x1, x2])
        .range([padding, width - padding]);
    let yscale = d3.scaleLinear()
        .domain([y1, y2])
        .range([height - padding, padding]);

    let xaxis = d3.axisBottom().scale(xscale);
    let yaxis = d3.axisLeft().scale(yscale);
    div0.innerHTML = '';
    let svg = d3.select('#graph0')
        .append('svg')
        .attr('width', width)
        .attr('height', height);

    svg.selectAll('line')
        .data([[x1, 0, x2, 0], [0, y1, 0, y2]].concat(lines))
        .enter()
        .append('line')
        .attr('x1', (d) => xscale(d[0]))
        .attr('y1', (d) => yscale(d[1]))
        .attr('x2', (d) => xscale(d[2]))
        .attr('y2', (d) => yscale(d[3]))
        .attr('stroke', (d) => d[4] || 'black');

    svg.selectAll('circle')
        .data(points)
        .enter()
        .append('circle')
        .attr('cx', (d) => xscale(d[0]))
        .attr('cy', (d) => yscale(d[1]))
        .attr('r', r)
        .attr('fill', (d) => d[2] || 'green');

    svg.append('g')
        .attr('transform', `translate(0, ${height - padding})`)
        .call(xaxis);

    svg.append('g')
        .attr('transform', `translate(${padding}, 0)`)
        .call(yaxis);

    [fns].forEach((fs) => p(fs.join('\n')));
};

inputs.forEach((input) => input.onchange = draw);
btn0.onclick = draw;
btn1.onclick = () => pre0.textContent = '';
draw();

r = dx =
x1 = x2 =
y1 = y2 =

Kamimura's blog

2018年10月20日土曜日

数学 - Python - JavaScript - 解析学 - 積分 - いくつかの計算練習 - (n!)^(1/n)の計算(階乗、累乗、極限)

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