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Last active March 6, 2019 05:07
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Contour Plot II
license: gpl-3.0
redirect: https://observablehq.com/@d3/contours
<!DOCTYPE html>
<svg width="960" height="500" stroke="#fff" stroke-width="0.5"></svg>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script src="https://d3js.org/d3-contour.v1.min.js"></script>
<script src="https://d3js.org/d3-scale-chromatic.v1.min.js"></script>
<script>
// Populate a grid of n×m values where -2 ≤ x ≤ 2 and -2 ≤ y ≤ 1.
var n = 240, m = 125, values = new Array(n * m);
for (var j = 0.5, k = 0; j < m; ++j) {
for (var i = 0.5; i < n; ++i, ++k) {
values[k] = goldsteinPrice(i / n * 4 - 2, 1 - j / m * 3);
}
}
var svg = d3.select("svg"),
width = +svg.attr("width"),
height = +svg.attr("height");
var thresholds = d3.range(1, 21)
.map(function(p) { return Math.pow(2, p); });
var contours = d3.contours()
.size([n, m])
.thresholds(thresholds);
var color = d3.scaleLog()
.domain(d3.extent(thresholds))
.interpolate(function() { return d3.interpolateYlGnBu; });
svg.selectAll("path")
.data(contours(values))
.enter().append("path")
.attr("d", d3.geoPath(d3.geoIdentity().scale(width / n)))
.attr("fill", function(d) { return color(d.value); });
// See https://en.wikipedia.org/wiki/Test_functions_for_optimization
function goldsteinPrice(x, y) {
return (1 + Math.pow(x + y + 1, 2) * (19 - 14 * x + 3 * x * x - 14 * y + 6 * x * x + 3 * y * y))
* (30 + Math.pow(2 * x - 3 * y, 2) * (18 - 32 * x + 12 * x * x + 48 * y - 36 * x * y + 27 * y * y));
}
</script>
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