## 2018年12月26日水曜日

### 数学 - Python - JavaScript - 解析学 - 積分 - 積分の応用 - 確率(確率密度関数(4次関数)、付随する確率関数(5次関数))

1. 定数 c を求める。

$\begin{array}{}{\int }_{0}^{1}c{x}^{4}\mathrm{dx}=\frac{1}{5}c\\ \frac{1}{5}c=1\\ c=5\end{array}$

よって、確率密度関数は、

$f\left(x\right)=5{x}^{4}$

確率関数は、

$\begin{array}{}f\left(x\right)\\ ={\int }_{0}^{x}5{t}^{4}\mathrm{dt}\\ ={x}^{5}\end{array}$

よって、 求める確率は、

$\begin{array}{}{\left(\frac{1}{2}\right)}^{5}\\ =\frac{1}{{2}^{5}}\\ =\frac{1}{32}\end{array}$

コード(Emacs)

Python 3

#!/usr/bin/env python3
from sympy import pprint, symbols, Integral, solve, Rational, plot

print('3.')

c, x = symbols('c, x')

f = c * x ** 4

eq = Integral(f, (x, 0, 1)) - 1
cs = solve(eq.doit(), c)

for t in [eq, cs]:
pprint(t)
print()

fc = f.subs({c: cs[0]})

I = Integral(fc, (x, 0, Rational(1, 2)))

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

p = plot(fc, ylim=(-10, 10), legend=True, show=False)

p.save('sample3.png')


$./sample3.py 3. 1 ⌠ ⎮ 4 ⎮ c⋅x dx - 1 ⌡ 0 [5] 1/2 ⌠ ⎮ 4 ⎮ 5⋅x dx ⌡ 0 1/32$


HTML5

<div id="graph0"></div>
<pre id="output0"></pre>
<label for="r0">r = </label>
<input id="r0" type="number" min="0" value="1">
<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">

<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,
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';

let fns = [[x => 5 * x ** 4, 'red']];

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, y1, 0, y2, 'green'],
[1 / 2, y1, 1 / 2, y2, 'blue'],
[1, y1, 1, y2, 'brown']];

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();