I'm a professor of mathematics at the University of North Carolina Asheville. I've also done a fair amount of consulting work over the years focusing on scientific and data visualization.
I'm happy to be part of the first Observable Ambassador's cohort.
A Julia set on the Riemann sphereThe Z-CurveBarnsley's fernA stochastic digraph IFS algorithmSelf-affine tilesThe TwindragonThe Eisenstein fractionsA self-affine tile with holesSelf-affine tiles via polygon mergeGolden rectangle fractalsBifurcation diagram with critical curvesThe tame twindragonIllustrations for the proof of Green's theoremNon-orientability of a Mobius stripExamples of parametric surfacesThe extended unit circlePenrose three coloringNewtons's method on the Riemann sphereConic sectionsDivisor graphsThe dance of Earth and VenusIterating multiples of the sine functionBorderline fractalsSelf-similar intersectionsBox-counting dimension examplesMandelbrot by dimensionInverse iteration for quadratic Julia setsInteger Apollonian PackingsIllustrations of two-dimensonal heat flowThe logistic bifurcation locusThe eleven unfoldings of the cubeA unimodal function with fractal level curvesGreen's theorem and polygonal areaThe geometry and numerics of first order ODEsThe xxx^xxx-spindleAnimated beatsRauzy FractalsHilbert's coordinate functionsPluckNot PiDrum strikeThe Koch snowflakeFractalized squareA Taylor series about π/4\pi/4π/4PlotX3D HyperboloidA PlotX3D animationModular arithmetic in 5th grade artSimple S-I-R ModelThe Poisson KernelPoly-gasketsClassification of 2D linear systems via trace and determinantJulia sets and the Mandelbrot setWater wavesFourier SeriesDisks for a solid of revolutionOrbit detection for the Mandelbrot setTracing a path on a spherePlot for mathematiciansFunctions of two variablesPartial derivativesDijkstra's algorithm on an RGGGradient ascentUnfolding polyhedraTangent plane to a level surfaceA strange discontinuityExamples of level surfacesMcMullen carpetsHills and valleysThe definition of ⇒Double and iterated integralsMST in an RGGTrees are bipartiteFractal typesettingd3.hierarchy and d3.treeK23 is PlanarPolar CoordinatesParametric region generatorParametric Plot 2DContour plotsGreedy graph coloringGraph6A few hundred interesting graphsThe Kings ProblemFirst order, autonomous systems of ODEsRunge-Kutta for systems of ODEs
Penrose tiling
function make_penrose_tiling() {
let svg_width = 800;
let svg_height = (2 * svg_width) / phi ** 2;
let xmin = 0;
let xmax = phi;
let ymin = -1 / phi;
let ymax = 1 / phi;
let svg = d3
.create("svg")
.style("max-width", `${svg_width}px`)
.attr("viewBox", [0, 0, svg_width, svg_height]);
// .attr("width", svg_width)
// .attr("height", svg_height);
let x_scale = d3.scaleLinear().domain([xmin, xmax]).range([0, svg_width]);
let y_scale = d3.scaleLinear().domain([ymin, ymax]).range([svg_height, 0]);
let pts_to_path = d3
.line()
.x(function (d) {
return x_scale(d[0]);
})
.y(function (d) {
return y_scale(d[1]);
});
svg
.selectAll("path")
.data(triangles)
.join("path")
// Piece together the triangles to form either Rhombs or Kites and Darts
// depending whether depth is odd or even
.attr("d", function (d) {
if (depth % 2 == 0) {
return pts_to_path([d.vertices[1], d.vertices[2], d.vertices[0]]);
} else {
if (d.type == "a") {
return pts_to_path([d.vertices[2], d.vertices[0], d.vertices[1]]);
} else {
return pts_to_path([d.vertices[0], d.vertices[1], d.vertices[2]]);
}
}
})
.attr("stroke", "black")
.attr("stroke-width", 1)
.attr("fill", function (d) {
if (d.type == "o") {
return "#B0B7BC";
} else {
return "#CE0F3D";
}
});
if (show_diag) {
svg
.selectAll("path.diag")
.data(triangles)
.join("path")
.attr("d", function (d) {
if (depth % 2 == 0) {
return pts_to_path([d.vertices[1], d.vertices[0]]);
} else {
if (d.type == "a") {
return pts_to_path([d.vertices[2], d.vertices[1]]);
} else {
return pts_to_path([d.vertices[0], d.vertices[2]]);
}
}
})
.attr("stroke", "black")
.attr("stroke-width", 0.6)
.attr("stroke-dasharray", "5,5")
.attr("fill", null);
} else {
svg
.selectAll("path.diag")
.data(triangles)
.join("path")
.attr("d", function (d) {
if (depth % 2 == 0) {
return pts_to_path([d.vertices[1], d.vertices[0]]);
} else {
if (d.type == "a") {
return pts_to_path([d.vertices[2], d.vertices[1]]);
} else {
return pts_to_path([d.vertices[0], d.vertices[2]]);
}
}
})
.attr("stroke", function (d) {
if (d.type == "o") {
return "#B0B7BC";
} else {
return "#CE0F3D";
}
})
.attr("stroke-width", 1)
.attr("fill", null);
}
return svg.node();
}
triangles = {
let triangles = [S];
for (let i = 0; i < depth; i++) {
triangles = triangles.map(dissect(i)).reduce(function(a, c) {
return a.concat(c);
}, []);
}
triangles = triangles.concat(
triangles.map(function(o) {
let newo = Object.assign({}, o);
newo.vertices = o.vertices.map(function(xy) {
let x = xy[0];
let y = -xy[1];
return [x, y];
});
return newo;
})
);
return triangles;
}
// When i is even, we dissect the acute triangles but
// when i is odd, we dissect the obtuse triangles.
function dissect(i) {
let i_dissect = function(T) {
let T1, T2;
let [p, q, r] = T.vertices;
if (T.type == 'a') {
if (i % 2 == 0) {
let new_point = [
(phi * q[0] + p[0]) * (2 - phi),
(phi * q[1] + p[1]) * (2 - phi)
];
T1 = {
vertices: [r, new_point, q],
type: 'a'
};
T2 = {
vertices: [r, new_point, p],
type: 'o'
};
return [T1, T2];
} else {
return [T];
}
} else if (T.type == 'o') {
if (i % 2 == 1) {
let new_point = [
(phi * r[0] + p[0]) * (2 - phi),
(phi * r[1] + p[1]) * (2 - phi)
];
T1 = {
vertices: [r, new_point, q],
type: 'o'
};
T2 = {
vertices: [p, q, new_point],
type: 'a'
};
return [T1, T2];
} else {
return [T];
}
}
};
return i_dissect;
}
// Start with a single obtuse triangle
S = ({
vertices: [[phi, 0], [phi / 2, Math.sin(Math.PI / 5)], [0, 0]],
type: 'o'
})
phi = (Math.sqrt(5) + 1) / 2
import { slider, checkbox } from "@jashkenas/inputs"
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