## 2018年6月20日水曜日

### 数学 - Python - JavaScript - 解析学 - 積分 - 積分の計算 - 三角関数の積分(連続関数、フーリエ係数、偶関数と奇関数、加法定理、正弦、余弦、倍角)

1. $\begin{array}{}{\int }_{-\pi }^{\pi }f\left(x\right)\mathrm{sin}\left(nx\right)\mathrm{dx}\\ ={\int }_{-\pi }^{0}f\left(x\right)\mathrm{sin}\left(nx\right)\mathrm{dx}+{\int }_{0}^{\pi }f\left(x\right)\mathrm{sin}\left(nx\right)\mathrm{dx}\\ =-{\int }_{0}^{-\pi }f\left(x\right)\mathrm{sin}\left(nx\right)\mathrm{dx}+{\int }_{0}^{\pi }f\left(x\right)\mathrm{sin}\left(nx\right)\mathrm{dx}\\ =-{\int }_{0}^{\pi }f\left(x\right)\mathrm{sin}\left(nx\right)\mathrm{dx}+{\int }_{0}^{\pi }f\left(x\right)\mathrm{sin}\left(nx\right)\mathrm{dx}\\ =0\\ {b}_{n}=0\end{array}$

2. $\begin{array}{}{c}_{0}=\frac{1}{2\pi }{\int }_{-\pi }^{\pi }f\left(x\right)\mathrm{dx}=0\\ {\int }_{-\pi }^{\pi }f\left(x\right)\mathrm{cos}\left(nx\right)\mathrm{dx}\\ ={\int }_{-\pi }^{0}f\left(x\right)\mathrm{cos}\left(nx\right)\mathrm{dx}+{\int }_{0}^{\pi }f\left(x\right)\mathrm{cos}\left(nx\right)\mathrm{dx}\\ =-{\int }_{0}^{-\pi }f\left(x\right)\mathrm{cos}\left(nx\right)\mathrm{dx}+{\int }_{0}^{\pi }f\left(x\right)\mathrm{cos}\left(nx\right)\mathrm{dx}\\ =-{\int }_{0}^{\pi }f\left(-x\right)\left(-\mathrm{cos}\left(nx\right)\right)\mathrm{dx}+{\int }_{0}^{\pi }f\left(x\right)\mathrm{cos}\left(nx\right)\mathrm{dx}\\ =-{\int }_{0}^{\pi }f\left(x\right)\mathrm{cos}\left(nx\right)\mathrm{dx}+{\int }_{0}^{\pi }f\left(x\right)\mathrm{cos}\left(nx\right)\mathrm{dx}\\ =0\\ {a}_{n}=0\\ {\int }_{-\pi }^{\pi }f\left(x\right)\mathrm{sin}\left(nx\right)\mathrm{dx}\\ ={\int }_{-\pi }^{0}f\left(x\right)\mathrm{sin}\left(nx\right)\mathrm{dx}+{\int }_{0}^{\pi }f\left(x\right)\mathrm{sin}\left(nx\right)\mathrm{dx}\\ =-{\int }_{0}^{-\pi }f\left(x\right)\mathrm{sin}\left(nx\right)\mathrm{dx}+{\int }_{0}^{\pi }f\left(x\right)\mathrm{sin}\left(nx\right)\mathrm{dx}\\ =-{\int }_{0}^{\pi }f\left(-x\right)\mathrm{sin}\left(nx\right)\mathrm{dx}+{\int }_{0}^{\pi }f\left(x\right)\mathrm{sin}\left(nx\right)\mathrm{dx}\\ ={\int }_{0}^{\pi }f\left(x\right)\mathrm{sin}\left(nx\right)\mathrm{dx}+{\int }_{0}^{\pi }f\left(x\right)\mathrm{sin}\left(nx\right)\mathrm{dx}\\ =2{\int }_{0}^{\pi }f\left(x\right)\mathrm{sin}\left(nx\right)\mathrm{dx}\\ {b}_{n}=\frac{2}{\pi }{\int }_{0}^{\pi }f\left(x\right)\mathrm{sin}\left(nx\right)\mathrm{dx}\end{array}$

コード(Emacs)

Python 3

#!/usr/bin/env python3
from sympy import pprint, symbols, pi, sin, cos, Integral, Function, plot

print('19.')
x = symbols('x')
n = symbols('n', positive=True, integer=True)

f = Function('f')(x)
c0 = 1 / (2 * pi) * Integral(f, (x, -pi, pi))
an = 1 / pi * Integral(f * cos(n * x), (x, -pi, pi))
bn = 1 / pi * Integral(f * sin(n * x), (x, -pi, pi))

fs = [c0, an, bn]

for i, h in enumerate([x ** 2, x]):
print(f'({chr(ord("a") + i)})')
for j, t in zip(['c0', 'an', 'bn'], fs):
print(f'{j}')
g = t.subs({f: h})
for s in [g, g.doit()]:
pprint(s)
print()
print()
print()

I = 2 / pi * Integral(x * sin(n * x), (x, 0, pi))
for t in [I, I.doit()]:
pprint(t)
print()

p = plot(x ** 2, x ** 2 * cos(2 * x), x ** 2 * sin(2 * x), x, x *
cos(2 * x), x * sin(2 * x), xlim=(-5, 5), legend=True, show=False)
colors = ['red', 'green', 'blue', 'orange', 'brown', 'purple']
for i, color in enumerate(colors):
p[i].line_color = color
p.save('sample26.svg')


$./sample26.py 19. (a) c0 π ⌠ ⎮ 2 ⎮ x dx ⌡ -π ──────── 2⋅π 2 π ── 3 an π ⌠ ⎮ 2 ⎮ x ⋅cos(n⋅x) dx ⌡ -π ───────────────── π n 4⋅(-1) ─────── 2 n bn π ⌠ ⎮ 2 ⎮ x ⋅sin(n⋅x) dx ⌡ -π ───────────────── π 0 (b) c0 π ⌠ ⎮ x dx ⌡ -π ─────── 2⋅π 0 an π ⌠ ⎮ x⋅cos(n⋅x) dx ⌡ -π ──────────────── π 0 bn π ⌠ ⎮ x⋅sin(n⋅x) dx ⌡ -π ──────────────── π n -2⋅(-1) ───────── n π ⌠ 2⋅⎮ x⋅sin(n⋅x) dx ⌡ 0 ───────────────── π n -2⋅(-1) ───────── n$


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="-10">
<label for="x2">x2 = </label>
<input id="x2" type="number" value="10">
<br>
<label for="y1">y1 = </label>
<input id="y1" type="number" value="-10">
<label for="y2">y2 = </label>
<input id="y2" type="number" value="10">
<br>
<label for="n0">n = </label>
<input id="n0" type="number" min="1" value="2">

<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="sample26.js"></script>


JavaScript

let div0 = document.querySelector('#graph0'),
pre0 = document.querySelector('#output0'),
width = 600,
height = 600,
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,
input_n0],
p = (x) => pre0.textContent += x + '\n';

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),
n0 = parseFloat(input_n0.value);

if (r === 0 || dx === 0 || x1 > x2 || y1 > y2) {
return;
}

let points = [],
lines = [[-Math.PI, y1, -Math.PI, y2, 'gray'],
[Math.PI, y1, Math.PI, y2, 'gray']],
fns = [[(x) => x ** 2, 'red'],
[(x) => x ** 2 * Math.cos(n0 * x), 'green'],
[(x) => x ** 2 * Math.sin(n0 * x), 'blue'],
[(x) => x, 'orange'],
[(x) => x * Math.cos(n0 * x), 'brown'],
[(x) => x * Math.sin(n0 * x), 'purple']];

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])
let yscale = d3.scaleLinear()
.domain([y1, y2])

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();