## 2017年10月24日火曜日

### 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 - 対数関数(曲線の描画、x軸とy軸との交点、導関数、二階導関数、凹凸)

1. $\begin{array}{l}y\text{'}=\frac{1}{-x}\left(-1\right)\\ =\frac{1}{x}\\ y\text{'}\text{'}=-\frac{1}{{x}^{2}}\\ 0=\mathrm{log}\left(-x\right)\\ -x=1\\ x=-1\end{array}$

2. $\begin{array}{l}y\text{'}=\frac{1}{2x}·2\\ =\frac{1}{x}\\ y\text{'}\text{'}=-\frac{1}{{x}^{2}}\\ 0=\mathrm{log}\left(2x\right)\\ 1=2x\\ x=\frac{1}{2}\end{array}$

3. $\begin{array}{l}y=\frac{1}{x+1}\\ y\text{'}\text{'}=-\frac{1}{{\left(x+1\right)}^{2}}\\ y=\mathrm{log}\left(0+1\right)\\ =\mathrm{log}1\\ =0\\ 0=\mathrm{log}\left(x+1\right)\\ 1=x+1\\ x=0\end{array}$

4. $\begin{array}{l}y\text{'}=\frac{1}{1-x}\left(-1\right)\\ =\frac{1}{x-1}\\ y\text{'}\text{'}=-\frac{1}{{\left(x-1\right)}^{2}}\\ y=\mathrm{log}\left(1-0\right)\\ =\mathrm{log}1\\ =0\\ 0=\mathrm{log}\left(1-x\right)\\ 1=1-x\\ x=0\end{array}$

5. $\begin{array}{l}y\text{'}=1-\frac{1}{x}\\ y\text{'}\text{'}=\frac{1}{{x}^{2}}\\ 0=x-\mathrm{log}x\end{array}$

コード(Emacs)

Python 3

#!/usr/bin/env python3
from sympy import pprint, symbols, log, plot

x = symbols('x')
fs = [(log(-x), (-10, 0)),
(log(2 * x), (0, 10)),
(log(x + 1), (-1, 9)),
(log(1 - x), (-9, 1)),
(x - log(x), (0, 10))]

for i, (f, (x1, x2)) in enumerate(fs, 19):
print(f'{i}.')
pprint(f)
print()
p = plot(log(x), f, (x, x1, x2), show=False, legend=True)
for j, color in enumerate(['red', 'green']):
p[j].line_color = color
p.save(f'sample{i}.svg')


$./sample19.py 19. log(-x) /opt/local/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/sympy/plotting/experimental_lambdify.py:232: UserWarning: The evaluation of the expression is problematic. We are trying a failback method that may still work. Please report this as a bug. warnings.warn('The evaluation of the expression is' 20. log(2⋅x) 21. log(x + 1) 22. log(-x + 1) 23. x - log(x)$


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="sample19.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 f = (x) => Math.log(x),
f19 = (x) => Math.log(-x),
f20 = (x) => Math.log(2 * x),
f21 = (x) => Math.log(x + 1),
f22 = (x) => Math.log(1 - x),
f23 = (x) => x - Math.log(x);

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 = [],
fns = [[f, 'red'],
[f19, 'green'],
[f20, 'blue'],
[f21, 'orange'],
[f22, 'brown'],
[f23, 'skyblue']]
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();