2018年12月12日水曜日

学習環境

解析入門(下) (松坂和夫 数学入門シリーズ 6) (松坂 和夫(著)、岩波書店)の第24章(重積分の変数変換)、24.2(変数変換定理)、問題5-(c).を取り組んでみる。



    1. 曲線がジオイドの内側の面積。(必要な範囲のみ)

      2 0 π 2 0 a 1 + cos θ r d r d θ = 0 π 2 r 2 0 a 1 + cos θ d θ = a 2 0 π 2 1 + cos θ 2 d θ = a 2 0 π 2 1 + 2 cos θ + cos 2 θ d θ = a 2 π 2 + 2 sin θ 0 π 2 + 1 2 cos θ sin θ 0 π 2 + 1 2 0 π 2 1 d θ = a 2 π 2 + 2 + 1 2 π 2 = a 2 2 + 3 4 π

      曲線カルジオイドの内側の曲線

      r = a

      の内側の面積。

      2 0 π 2 0 a r d r d θ = 0 π 2 r 2 0 a d θ = 0 π 2 a 2 d θ = π 2 a 2

      よって、求める面積は、

      a 2 2 + 3 4 π - π 2 a 2 = a 2 2 + π 4

コード(Emacs)

Python 3

#!/usr/bin/env python3
from sympy import pprint, symbols, Integral, pi, cos, sqrt, Rational

print('5-(c).')

r, theta, a = symbols('r, θ, a')

I = 2 * Integral(Integral(r, (r, a, a * (1 + cos(theta)))),
                 (theta, 0, pi / 2))


for t in [I, I.doit(), I.doit().simplify()]:
    pprint(t)
    print()

入出力結果(Terminal, Jupyter(IPython))

$ ./sample5.py
5-(c).
  π                       
  ─                       
  2 a⋅(cos(θ) + 1)        
  ⌠       ⌠               
2⋅⎮       ⎮        r dr dθ
  ⌡       ⌡               
  0       a               

     2               
  π⋅a     2 ⎛    3⋅π⎞
- ──── + a ⋅⎜2 + ───⎟
   2        ⎝     4 ⎠

 2        
a ⋅(π + 8)
──────────
    4     

$

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="0.0001" value="0.005">
<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="sample5.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 a = 2,
    fr = theta => a * (1 + Math.cos(theta)),
    fr1 = theta => a;
    fns = [];

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 = [];

    for (let theta = 0; theta < 2 * Math.PI; theta += dx) {
        let r0 = fr(theta),
            r1 = fr1(theta);
        
        points.push([r0 * Math.cos(theta), r0 * Math.sin(theta), 'red']);
        points.push([r1 * Math.cos(theta), r1 * Math.sin(theta), 'green']);
    }
    
    fns
        .forEach((o) => {
            let [fn, color] = o;
            
            for (let x = x1; x <= x2; x += dx) {
                let y = fn(x);
                
                if (Math.abs(y) < Infinity) {
                    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('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.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.append('g')
        .attr('transform', `translate(0, ${height - padding})`)
        .call(xaxis);

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

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







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