2017年10月25日水曜日

学習環境

解析入門 原書第3版 (S.ラング(著)、松坂 和夫(翻訳)、片山 孝次(翻訳)、岩波書店)の第2部(微分と基本的な関数)、第8章(指数関数と対数関数)、1(対数関数)、練習問題24、25.を取り組んでみる。


  1. b n =a log b n =loga nlogb=loga logb= 1 n loga

  2. 関数logx の2階微分について。

    d dx logx= 1 x d 2 d x 2 logx= 1 x 2 <0

    よって、関数log x は上に凸である。

    第6章の3の問題12より。

    i=1 n 1 n log a i log( i=1 n 1 n a i ) 1 n i=1 n log a i log( i=1 n 1 n a i ) 1 n log i=1 n a i log( i=1 n a i n ) log ( i=1 n a i ) 1 n log( i=1 n a i n )

    また、log x は増加関数。

    d dx logx>0

    よって、問題の不等式が成り立つ。

    ( i=1 n a i ) 1 n ( i=1 n a i n )

コード(Emacs)

Python 3

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

print('24.')
x = symbols('x')
i, n = symbols('i n', integer=True)
l = product(i, (i, 1, n)) ** (1 / n)
r = summation(i, (i, 1, n)) / n

for t in [l, r]:
    pprint(t)
    print()

for n0 in range(1, 10):
    print(f'n = {n0}')
    for t in [l.subs({n: n0}), r.subs({n: n0}), l.subs({n: n0}) <= r.subs({n: n0})]:
        pprint(t)
    print()

入出力結果(Terminal, Jupyter(IPython))

$ ./sample24.py
24.
n ____
╲╱ n! 

 2    
n    n
── + ─
2    2
──────
  n   

n = 1
1
1
True

n = 2
√2
3/2
True

n = 3
3 ___
╲╱ 6 
2
True

n = 4
4 ____
╲╱ 24 
5/2
True

n = 5
5 _____
╲╱ 120 
3
True

n = 6
 2/3 3 ___ 6 ___
2   ⋅╲╱ 3 ⋅╲╱ 5 
7/2
True

n = 7
7 ______
╲╱ 5040 
4
True

n = 8
4 ___ 8 ______
╲╱ 3 ⋅╲╱ 4480 
9/2
True

n = 9
9 ________
╲╱ 362880 
5
True

$

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="-0">
<label for="x2">x2 = </label>
<input id="x2" type="number" value="20">
<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="sample24.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 f = (x) =>
    range(1, Math.floor(x) + 1)
    .reduce((prev, next) => prev * next, 1) ** (1 / Math.floor(x)),
    g = (x) => 
    range(1, Math.floor(x) + 1)
    .reduce((prev, next) => prev + next, 0) / Math.floor(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, 'green'],
               [g, 'blue']],
        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])
        .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('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();







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