## 2018年2月8日木曜日

### 数学 - Python - JavaScript - 図形の変換の方法 - 線形写像・1次変換 – 1次変換による色々な図形の像 - 1次変換よって面積はどのように変わるか？(平行四辺形、行列式の絶対値倍)

1. $\left(\begin{array}{cc}2& -1\\ -2& 3\end{array}\right)\left(\begin{array}{cc}1& 3\\ 1& -3\end{array}\right)=\left(\begin{array}{cc}1& 9\\ 1& -15\end{array}\right)$
$\stackrel{\to }{a}\text{'}=\left(\begin{array}{c}1\\ 1\end{array}\right),\stackrel{\to }{b}\text{'}=\left(\begin{array}{c}9\\ -15\end{array}\right)$
$\left|\mathrm{det}\left(\begin{array}{cc}1& 3\\ 1& -3\end{array}\right)\right|=\left|-3-3\right|=6$
$\left|\mathrm{det}\left(\begin{array}{cc}1& 9\\ 1& -15\end{array}\right)\right|=\left|-15-9\right|=24$
$\left|\mathrm{det}\left(\begin{array}{cc}2& -1\\ -2& 3\end{array}\right)\right|=\left|6-2\right|=4$
$6·4=24$

よって、平行四辺形の面積は行列式の絶対値倍になっている。

コード(Emacs)

Python 3

#!/usr/bin/env python3
from sympy import pprint, Matrix

points = [(1, 1), (3, -3)]
A = Matrix([[2, -1],
[-2, 3]])
for p in points:
X = Matrix(p).reshape(2, 1)
for t in [X, A * X]:
pprint(t.T)
print()
print()


$./sample20.py [1 1] [1 1] [3 -3] [9 -15]$


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="0.005">
<br>
<label for="x1">x1 = </label>
<input id="x1" type="number" value="-15">
<label for="x2">x2 = </label>
<input id="x2" type="number" value="15">
<br>
<label for="y1">y1 = </label>
<input id="y1" type="number" value="-15">
<label for="y2">y2 = </label>
<input id="y2" type="number" value="15">

<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="sample20.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'),
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 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 = [[0, 0, 1, 1,'red'],
[1, 1, 4, -2, 'green'],
[4, -2, 3, -3, 'blue'],
[3, -3, 0, 0, 'orange'],
[0, 0, 1, 1, 'purple'],
[1, 1, 10, -14, 'brown'],
[10, -14, 9, -15, 'gray'],
[9, -15, 0, 0, 'pink']],
fns = [],
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])
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, fns1, fns2].forEach((fs) => p(fs.join('\n')));
};

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