source: Dev/trunk/d3/examples/chord/chord.js @ 76

// From http://mkweb.bcgsc.ca/circos/guide/tables/
var chord = d3.layout.chord()
  .padding(.05)
  .sortSubgroups(d3.descending)
  .matrix([
    [11975,  5871, 8916, 2868],
    [ 1951, 10048, 2060, 6171],
    [ 8010, 16145, 8090, 8045],
    [ 1013,   990,  940, 6907]
  ]);

var w = 600,
    h = 600,
    r0 = Math.min(w, h) * .41,
    r1 = r0 * 1.1;

var fill = d3.scale.ordinal()
    .domain(d3.range(4))
    .range(["#000000", "#FFDD89", "#957244", "#F26223"]);

var svg = d3.select("#chart")
  .append("svg:svg")
    .attr("width", w)
    .attr("height", h)
  .append("svg:g")
    .attr("transform", "translate(" + w / 2 + "," + h / 2 + ")");

svg.append("svg:g")
  .selectAll("path")
    .data(chord.groups)
  .enter().append("svg:path")
    .style("fill", function(d) { return fill(d.index); })
    .style("stroke", function(d) { return fill(d.index); })
    .attr("d", d3.svg.arc().innerRadius(r0).outerRadius(r1))
    .on("mouseover", fade(.1))
    .on("mouseout", fade(1));

var ticks = svg.append("svg:g")
  .selectAll("g")
    .data(chord.groups)
  .enter().append("svg:g")
  .selectAll("g")
    .data(groupTicks)
  .enter().append("svg:g")
    .attr("transform", function(d) {
      return "rotate(" + (d.angle * 180 / Math.PI - 90) + ")"
          + "translate(" + r1 + ",0)";
    });

ticks.append("svg:line")
    .attr("x1", 1)
    .attr("y1", 0)
    .attr("x2", 5)
    .attr("y2", 0)
    .style("stroke", "#000");

ticks.append("svg:text")
    .attr("x", 8)
    .attr("dy", ".35em")
    .attr("text-anchor", function(d) {
      return d.angle > Math.PI ? "end" : null;
    })
    .attr("transform", function(d) {
      return d.angle > Math.PI ? "rotate(180)translate(-16)" : null;
    })
    .text(function(d) { return d.label; });

svg.append("svg:g")
    .attr("class", "chord")
  .selectAll("path")
    .data(chord.chords)
  .enter().append("svg:path")
    .style("fill", function(d) { return fill(d.target.index); })
    .attr("d", d3.svg.chord().radius(r0))
    .style("opacity", 1);

/** Returns an array of tick angles and labels, given a group. */
function groupTicks(d) {
  var k = (d.endAngle - d.startAngle) / d.value;
  return d3.range(0, d.value, 1000).map(function(v, i) {
    return {
      angle: v * k + d.startAngle,
      label: i % 5 ? null : v / 1000 + "k"
    };
  });
}

/** Returns an event handler for fading a given chord group. */
function fade(opacity) {
  return function(g, i) {
    svg.selectAll("g.chord path")
        .filter(function(d) {
          return d.source.index != i && d.target.index != i;
        })
      .transition()
        .style("opacity", opacity);
  };
}