eliangcs · January 18, 2016 06:44
diff --git a/index.html b/index.html
 <!DOCTYPE html>
 <meta charset="utf-8">
 <style>

 .svg {
    border: 1px solid #000;
 }

 .result {
    color: #05c;
 }

 </style>
 <body>

 <div class="result"></div>

 <script src="//d3js.org/d3.v3.min.js"></script>
 <script>

 var width = 540,
    height = 320,
    xmin = 0,
    xmax = Math.PI,
    ymin = 0,
    ymax = 1.0,
    xscale = d3.scale.linear(),
    yscale = d3.scale.linear(),
    sine = d3.svg.line(),
    svg = d3.select('body').append('svg'),
    decor = svg.append('g'),
    graph = svg.append('g'),
    sampleSize = 100,
    sampleCount = 0,
    delay = 10,
    integral = 0.0;

 function reset() {
    integral = 0.0;
    sampleCount = 0;
    graph.selectAll('*').remove();
    integralResult.text('-');
 }

 xscale.domain([xmin, xmax])
      .range([0, width]);

 yscale.domain([ymin, ymax])
      .range([height, 0]);

 svg.attr({
    width: width,
    height: height,
    class: 'svg'
 });

 function draw(x, y, area) {
    var h = y;
    var w = area / h;
    x = xscale(x - w * 0.5);
    y = yscale(y);
    w = xscale(w);
    graph.append('rect').attr({
        x: x,
        y: y,
        width: w,
        height: height - y,
        fill: '#06c',
        opacity: 0.2
    });
 }

 // The function f(x) we're integrating
 function f(x) {
    if (x >= 0.0 && x <= Math.PI) {
        return Math.sin(x);
    }
    return 0.0;
 }

 // The probability density of a sample x
 function p(x) {
    // Uniform distribution over [0, PI]
    return 1.0 / Math.PI;
 }

 // Given a current location x, propose a new location x2
 function mutate(x) {
    // Uniform sampling over [0, PI]
    return Math.random() * Math.PI;
 }

 // Given the current location x, what's the probability that the algorithm
 // accepts the new location x2
 function accept(x, x2) {
    // return 1;
    return Math.min(1.0, p(x2) / p(x));
 }

 // Metropolis algorithm
 function sample(x) {
    var x2 = mutate(x);
    var a = accept(x, x2);
    if (Math.random() < a) {
        x = x2;
    }

    var y = f(x);
    var d = y / (p(x) * sampleSize);
    integral += d;

    draw(x, y, d);

    sampleCount++;
    if (sampleCount < sampleSize) {
        setTimeout(function() {
            sample(x);
        }, delay);
    } else {
        d3.select('.result').text('Integral: ' + integral);
    }
 }

 var x0 = Math.random() * Math.PI;
 sample(x0);

 </script>
	<!DOCTYPE html>
	<meta charset="utf-8">
	<style>

	.svg {
	border: 1px solid #000;
	}

	.result {
	color: #05c;
	}

	</style>
	<body>

	<div class="result"></div>

	<script src="//d3js.org/d3.v3.min.js"></script>
	<script>

	var width = 540,
	height = 320,
	xmin = 0,
	xmax = Math.PI,
	ymin = 0,
	ymax = 1.0,
	xscale = d3.scale.linear(),
	yscale = d3.scale.linear(),
	sine = d3.svg.line(),
	svg = d3.select('body').append('svg'),
	decor = svg.append('g'),
	graph = svg.append('g'),
	sampleSize = 100,
	sampleCount = 0,
	delay = 10,
	integral = 0.0;

	function reset() {
	integral = 0.0;
	sampleCount = 0;
	graph.selectAll('*').remove();
	integralResult.text('-');
	}

	xscale.domain([xmin, xmax])
	.range([0, width]);

	yscale.domain([ymin, ymax])
	.range([height, 0]);

	svg.attr({
	width: width,
	height: height,
	class: 'svg'
	});

	function draw(x, y, area) {
	var h = y;
	var w = area / h;
	x = xscale(x - w * 0.5);
	y = yscale(y);
	w = xscale(w);
	graph.append('rect').attr({
	x: x,
	y: y,
	width: w,
	height: height - y,
	fill: '#06c',
	opacity: 0.2
	});
	}

	// The function f(x) we're integrating
	function f(x) {
	if (x >= 0.0 && x <= Math.PI) {
	return Math.sin(x);
	}
	return 0.0;
	}

	// The probability density of a sample x
	function p(x) {
	// Uniform distribution over [0, PI]
	return 1.0 / Math.PI;
	}

	// Given a current location x, propose a new location x2
	function mutate(x) {
	// Uniform sampling over [0, PI]
	return Math.random() * Math.PI;
	}

	// Given the current location x, what's the probability that the algorithm
	// accepts the new location x2
	function accept(x, x2) {
	// return 1;
	return Math.min(1.0, p(x2) / p(x));
	}

	// Metropolis algorithm
	function sample(x) {
	var x2 = mutate(x);
	var a = accept(x, x2);
	if (Math.random() < a) {
	x = x2;
	}

	var y = f(x);
	var d = y / (p(x) * sampleSize);
	integral += d;

	draw(x, y, d);

	sampleCount++;
	if (sampleCount < sampleSize) {
	setTimeout(function() {
	sample(x);
	}, delay);
	} else {
	d3.select('.result').text('Integral: ' + integral);
	}
	}

	var x0 = Math.random() * Math.PI;
	sample(x0);

	</script>