341 lines
7.0 KiB
JavaScript
341 lines
7.0 KiB
JavaScript
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//testbed for playing with stuff in node repl
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const THREE =require('three');
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function pandita(a) {
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const n = a.length;
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for( let k = n - 2; k >= 0; k-- ) {
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if( a[k] < a[k + 1] ) {
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for( let l = n - 1; l >= 0; l-- ) {
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if( a[k] < a[l] ) {
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const tmp = a[k];
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a[k] = a[l];
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a[l] = tmp;
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const revtail = a.slice(k + 1);
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revtail.reverse();
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for( let i = 0; i < revtail.length; i++ ) {
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a[k + 1 + i] = revtail[i];
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}
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return Math.floor(revtail.length / 2) + 1;
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}
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}
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console.log("Shouldn't get here");
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process.exit();
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}
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}
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return false;
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}
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function permutations_old(a) {
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a.sort();
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const ps = [ [...a] ];
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let running = true;
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while( running ) {
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const s = pandita(a);
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if( s ) {
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ps.push([...a]);
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} else {
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running = false;
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}
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}
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return ps;
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}
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function permutations(a) {
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a.sort();
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const ps = [ [...a] ];
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let running = true;
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while( pandita(a) > 0 ) {
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ps.push([...a]);
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}
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return ps;
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}
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function permutations_even(a) {
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a.sort();
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let parity = 'even';
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const ps = [ [...a] ];
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let running = true;
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while( running ) {
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const s = pandita(a);
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if( s ) {
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if( parity === 'even' ) {
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if( s % 2 === 1 ) {
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parity = 'odd';
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}
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} else {
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if( s % 2 === 1 ) {
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parity = 'even';
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}
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}
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if( parity === 'even' ) {
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ps.push([...a]);
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}
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} else {
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running = false;
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}
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}
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return ps;
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}
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// for a given permutation, say [ 1, 1, 0, 0 ], return all
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// of the valid changes of sign, so:
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// [ [1, 1, 0, 0 ], [ -1, 1, 0, 0 ], [ 1, -1, 0, 0 ], [-1, -1, 0, 0 ]]
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// ie don't do it on the zeros
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function expand_sign(a, label) {
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const expanded = [];
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const exv = a.map((v) => v ? [ -v, v ] : [ 0 ]);
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for( const xv of exv[0] ) {
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for( const yv of exv[1] ) {
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for( const zv of exv[2] ) {
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for( const wv of exv[3] ) {
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expanded.push({label: label, x: xv, y:yv, z:zv, w:wv});
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}
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}
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}
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}
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return expanded;
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}
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function coordinates(a, id0=1, even=false) {
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const ps = even ? permutations_even(a) : permutations(a);
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const coords = [];
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for( const p of ps ) {
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const expanded = expand_sign(p, 0);
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coords.push(...expanded);
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}
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return coords;
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}
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function index_nodes(nodes, scale) {
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let i = 1;
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for( const n of nodes ) {
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n["id"] = i;
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i++;
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}
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}
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function scale_nodes(nodes, scale) {
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for( const n of nodes ) {
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for( const a of [ 'x', 'y', 'z', 'w' ] ) {
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n[a] = scale * n[a];
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}
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}
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}
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function dist2(n1, n2) {
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return (n1.x - n2.x) ** 2 + (n1.y - n2.y) ** 2 + (n1.z - n2.z) ** 2 + (n1.w - n2.w) ** 2;
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}
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function auto_detect_edges(nodes, neighbours, debug=false) {
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const seen = {};
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const nnodes = nodes.length;
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const links = [];
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let id = 1;
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for( const n1 of nodes ) {
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const d2 = [];
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for( const n2 of nodes ) {
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d2.push({ d2: dist2(n1, n2), id: n2.id });
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}
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d2.sort((a, b) => a.d2 - b.d2);
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const closest = d2.slice(1, neighbours + 1);
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if( debug ) {
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console.log(`closest = ${closest.length}`);
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console.log(closest);
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}
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for( const e of closest ) {
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const ids = [ n1.id, e.id ];
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ids.sort();
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const fp = ids.join(',');
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if( !seen[fp] ) {
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seen[fp] = true;
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links.push({ id: id, label: 0, source: n1.id, target: e.id });
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id++;
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}
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}
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}
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if( debug ) {
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console.log(`Found ${links.length} edges`)
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}
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return links;
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}
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function make_120cell_vertices() {
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const phi = 0.5 * (1 + Math.sqrt(5));
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const r5 = Math.sqrt(5);
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const phi2 = phi * phi;
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const phiinv = 1 / phi;
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const phi2inv = 1 / phi2;
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const nodes = [
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coordinates([0, 0, 2, 2], 0),
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coordinates([1, 1, 1, r5], 0),
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coordinates([phi, phi, phi, phi2inv], 0),
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coordinates([phiinv, phiinv, phiinv, phi2], 0),
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coordinates([phi2, phi2inv, 1, 0], 0, true),
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coordinates([r5, phiinv, phi, 0], 0, true),
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coordinates([2, 1, phi, phiinv], 0, true),
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].flat();
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index_nodes(nodes);
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// scale_nodes(nodes, 0.5);
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return nodes;
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}
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// face detection for the 120-cell
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// NOTE: all of these return node ids, not nodes
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// return all the links which connect to a node
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function nodes_links(links, nodeid) {
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return links.filter((l) => l.source === nodeid || l.target === nodeid);
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}
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// filter to remove a link to a given id from a set of links
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function not_to_this(link, nodeid) {
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return !(link.source === nodeid || link.target === nodeid);
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}
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// given nodes n1, n2, return all neighbours of n2 which are not n1
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function unmutuals(links, n1id, n2id) {
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const nlinks = nodes_links(links, n2id).filter((l) => not_to_this(l, n1id));
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return nlinks.map((l) => {
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if( l.source === n2id ) {
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return l.target;
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} else {
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return l.source;
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}
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})
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}
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function fingerprint(ids) {
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const sids = [...ids];
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sids.sort();
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return sids.join(',');
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}
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function auto_120cell_faces(links) {
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const faces = [];
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const seen = {};
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let id = 1;
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for( const edge of links ) {
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const v1 = edge.source;
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const v2 = edge.target;
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const n1 = unmutuals(links, v2, v1);
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const n2 = unmutuals(links, v1, v2);
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const shared = [];
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for( const a of n1 ) {
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const an = unmutuals(links, v1, a);
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for( const d of n2 ) {
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const dn = unmutuals(links, v2, d);
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for( const x of an ) {
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for( const y of dn ) {
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if( x == y ) {
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shared.push([v1, a, x, d, v2])
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}
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}
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}
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}
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}
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if( shared.length !== 3 ) {
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console.log(`Bad shared faces for ${edge.id} ${v1} ${v2}`);
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}
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for( const face of shared ) {
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const fp = fingerprint(face);
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if( !seen[fp] ) {
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faces.push({ id: id, edge: edge.id, v1: edge.source, v2: edge.target, fingerprint: fp, nodes: face });
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id++;
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seen[fp] = true;
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}
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}
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}
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return faces;
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}
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// trying to go from faces to dodecahedra
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function shared_vertices(f1, f2) {
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return f1.nodes.filter((f) => f2.nodes.includes(f));
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}
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function adjacent_faces(f1, f2) {
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// adjacent faces which share an edge, not just a vertex
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const intersect = shared_vertices(f1, f2);
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if( intersect.length < 2 ) {
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return false;
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}
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if( intersect.length > 2 ) {
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console.log(`warning: faces ${f1.id} and ${f2.id} have too many common vertices`);
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}
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return true;
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}
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function find_adjacent_faces(faces, face) {
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const neighbours = faces.filter((f) => f.id !== face.id && adjacent_faces(f, face));
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return neighbours;
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}
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function find_dodeca_mutuals(faces, f1, f2) {
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// for any two adjacent faces, find their common neighbours where
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// all three share exactly one vertex (this, I think, guarantees that
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// all are on the same dodecahedron)
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const n1 = find_adjacent_faces(faces, f1);
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const n2 = find_adjacent_faces(faces, f2);
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const common = n1.filter((f1) => n2.filter((f2) => f1.id === f2.id).length > 0 );
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// there's one extra here - the third which has two nodes in common with
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// both f1 and f2 - filter it out
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const mutuals = common.filter((cf) => {
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const shared = cf.nodes.filter((n) => f1.nodes.includes(n) && f2.nodes.includes(n));
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return shared.length === 1
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});
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return mutuals;
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}
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const cell120 = () => {
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const nodes = make_120cell_vertices();
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const links = auto_detect_edges(nodes, 4);
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return {
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nodes: nodes,
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links: links,
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geometry: {
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node_size: 0.02,
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link_size: 0.02
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}
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}
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}
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const nodes = make_120cell_vertices();
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const links = auto_detect_edges(nodes, 4);
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const faces = auto_120cell_faces(links);
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