数学 - Python - JavaScript - 解析学 - 微分と基本的な関数 - 指数関数と対数関数 - 大きさの程度(2乗乗、符号、導関数、二階微分、極値、変曲点、関数の凹凸、グラフの描画)

解析入門 原書第3版
原著

学習環境

• Surface 3 (4G LTE)、Surface 3 タイプ カバー、Surface ペン(端末)
• Windows 10 Pro (OS)
• Nebo(Windows アプリ)
• iPad Pro + Apple Pencil
• MyScript Nebo(iPad アプリ)
• 参考書籍
  • Pythonからはじめる数学入門
  • JavaScriptリファレンス 第6版
  • インタラクティブ・データビジュアライゼーション

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2部(微分と基本的な関数)、第8章(指数関数と対数関数)、4(大きさの程度)、練習問題3.を取り組んでみる。

3. 
   
   $\begin{array}{}f\text{'}\left(x\right)\\ =e^{-x^2}+x{e}^{-x^2}\left(-2x\right)\\ =e^{-x^2}-2x^2{e}^{-x^2}\\ =e^{-x^2}\left(1-2x^2\right)\end{array}$
   $\begin{array}{}f\text{'}\text{'}\left(x\right)\\ =e^{-x^2}\left(-2x\right)-4x{e}^{-x^2}-2x^2{e}^{-x^2}\left(-2x\right)\\ =-2x{e}^{-x^2}-4x{e}^{-x^2}+4x^3{e}^{-x^2}\\ =-6x{e}^{-x^2}+4x^3{e}^{-x^2}\\ =2x{e}^{-x^2}\left(2x^2-3\right)\end{array}$
   $\begin{array}{}f\text{'}\left(x\right)=0\\ 1-2x^2=0\\ x=\pm \; <!--\; plus-minus\; sign\; -->\frac{1}{\sqrt{2}}\end{array}$
   $\begin{array}{}f\text{'}\text{'}\left(x\right)=0\\ x=0,\pm \; <!--\; plus-minus\; sign\; -->\sqrt{\frac{3}{2}}\\ x=0,\pm \; <!--\; plus-minus\; sign\; -->\frac{\sqrt{6}}{2}\end{array}$
   $f\left(0\right)=0$
   $\begin{array}{}\underset{x\to \; <!--\; rightwards\; arrow\; -->\mathrm{\infty \; <!--\; infinity\; -->}}{\lim }f\left(x\right)=0\\ \underset{x\to \; <!--\; rightwards\; arrow\; -->-\mathrm{\infty \; <!--\; infinity\; -->}}{\lim }f\left(x\right)=0\end{array}$

   関数のグラフの描画。

コード(Emacs)

Python 3

#!/usr/bin/env python3
from sympy import pprint, symbols, exp, Derivative, solve, plot

x = symbols('x')
f = x * exp(-x ** 2)
f1 = Derivative(f, x, 1).doit()
f2 = Derivative(f, x, 2).doit()

for g in [f, f1, f2]:
    for t in [g, solve(g)]:
        pprint(t)
        print()
    print()


p = plot(f, (x, -5, 5), ylim=(-2, 2), show=False, legend=True)

p.save('sample3.svg')

入出力結果(Terminal, Jupyter(IPython))

$ ./sample2.py
d ⎛   -x⎞
──⎝x⋅ℯ  ⎠
dx       

     -x    -x
- x⋅ℯ   + ℯ  


  2       
 d ⎛   -x⎞
───⎝x⋅ℯ  ⎠
  2       
dx        

         -x
(x - 2)⋅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="0.001">
<br>
<label for="x1">x1 = </label>
<input id="x1" type="number" value="-5">
<label for="x2">x2 = </label>
<input id="x2" type="number" value="5">
<br>
<label for="y1">y1 = </label>
<input id="y1" type="number" value="-5">
<label for="y2">y2 = </label>
<input id="y2" type="number" value="5">

<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="sample3.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'),
    inputs = [input_r, input_dx, input_x1, input_x2, input_y1, input_y2],
    p = (x) => pre0.textContent += x + '\n',
    range = (start, end, step=1) => {
        let res = [];
        for (let i = start; i < end; i += step) {
            res.push(i);
        }
        return res;
    };

let f = (x) => x * Math.exp(-(x ** 2)),
    f1 = (x) => Math.exp(- (x ** 2)) * (1 - 2 * x ** 2),
    f2 = (x) => 2 * x * Math.exp(- (x ** 2)) * (2 * x ** 2 - 3);

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 = [[1 / Math.sqrt(2), y1, 1 / Math.sqrt(2), y2, 'red'],
                 [- 1 / Math.sqrt(2), y1, - 1 / Math.sqrt(2), y2, 'red'],
                 [Math.sqrt(6) / 2, y1, Math.sqrt(6) / 2, y2, 'brown'],
                 [Math.sqrt(6) / 2, y1, Math.sqrt(6) / 2, y2, 'brown'],
                 [0, y1, 0, y2, 'brown']],
        fns = [[f, 'green'],
               [f1, 'blue'],
               [f2, 'orange']],
        fns1 = [],
        fns2 = [];

    fns
        .forEach((o) => {
            let [f, color] = o;
            for (let x = x1; x <= x2; x += dx) {
                let y = f(x);

                points.push([x, y, color]);
            }
        });

    fns1
        .forEach((o) => {
            let [f, color] = o;
            
            lines.push([x1, f(x1), x2, f(x2), color]);
        });
        
    fns2
        .forEach((o) => {
           let [f, color] = o;

            for (let x = x1; x <= x2; x += dx0) {
                let g = f(x);
                lines.push([x1, g(x1), x2, g(x2), 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, fns1, fns2].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 =