30:[] 2e:{"title":"Accretion","cells":[{"id":0,"value":"# Accretion\n\nSimulation of accretion of particles attracted by electrostatic or gravitational forces, analogous to the interaction within dust clouds found in the early stages of star formation.\n\nUses D3's force plugin [forceMagnetic](https://github.com/vasturiano/d3-force-magnetic) to simulate the attraction/repulsion of objects of varying mass in an [inverse-square relationship](https://en.wikipedia.org/wiki/Inverse-square_law) with distance.\nFurther, particles are prevented from overlapping by applying a non-elastic collision force using [forceBounce](https://github.com/vasturiano/d3-force-bounce). \n\nUsing the slider controls you can add/remove particles to the system, and regulate the ratio of attractive (green attracts all other) vs repellent (red repels all other).","pinned":false,"hidden":false,"mode":"md"},{"id":17,"value":"viewof particleDensity = slider({\n min: 0, \n max: 1000, \n step: 10,\n value: 200,\n format: v => `${v} particles/kpx²`,\n title: 'Density'\n})","pinned":false,"hidden":false,"mode":"ojs"},{"id":29,"value":"viewof probAttraction = slider({\n min: 0, \n max: 1, \n step: 0.01,\n value: 1,\n format: v => html`${Math.round((1 - v) * 100)}% repellent | ${Math.round(v * 100)}% attractive`,\n title: 'Attraction'\n})","pinned":false,"hidden":false,"mode":"ojs"},{"id":5,"value":"domEl = html`

`;","pinned":false,"hidden":false,"mode":"ojs"},{"id":8,"value":"pod = { \n const pod = d3ForcePod()(domEl)\n .nodeColor(({ pole }) => COLORS[pole > 0 ? 'attractive' : 'repellent']);\n\n // Add collision force\n pod.addForce(d3.forceBounce()\n\t\t.radius(d => d.r)\n\t\t.elasticity(0)\n\t);\n\n // Add attraction force\n\tpod.addForce(d3.forceMagnetic()\n\t\t.charge(node => node.pole * node.r * node.r)\n\t\t.strength(ACCELERATION_K)\n\t);\n \n return pod;\n}","pinned":true,"hidden":false,"mode":"ojs"},{"id":65,"value":"nodes = {\n const numParticles = Math.round(pod.width() * pod.height() * particleDensity / 1e6), // control in kpx^2\n\t\texistingParticles = pod.nodes();\n\n const nodes = numParticles === existingParticles.length\n // Keep as is\n ? existingParticles\n : (numParticles < existingParticles.length)\n // Trim\n ? existingParticles.slice(0, numParticles)\n // Append\n : [...existingParticles, ...[...new Array(numParticles - existingParticles.length)].map(() => ({\n \t\t\tx: Math.random() * pod.width(),\n \t\t\ty: Math.random() * pod.height(),\n \t\t\tr: Math.round(Math.random() * (PARTICLE_RADIUS_RANGE[1] - PARTICLE_RADIUS_RANGE[0]) + PARTICLE_RADIUS_RANGE[0])\n\t\t })\n )];\n\n\tconst negThreshold = Math.floor(probAttraction * numParticles);\n\tnodes.forEach((node, i) => node.pole = i < negThreshold ? 1 : -1);\n\n pod.nodes(nodes);\n\n return nodes;\n}","pinned":false,"hidden":false,"mode":"ojs"},{"id":181,"value":"**Container**","pinned":false,"hidden":false,"mode":"md"},{"id":102,"value":"height = {\n const height = Math.min(MAX_HEIGHT, width / ASPECT_RATIO);\n \n pod.width(width).height(height);\n \n return height;\n}","pinned":false,"hidden":false,"mode":"ojs"},{"id":10,"value":"**Constants**","pinned":false,"hidden":false,"mode":"md"},{"id":112,"value":"ASPECT_RATIO = 16 / 9;","pinned":false,"hidden":false,"mode":"ojs"},{"id":138,"value":"MAX_HEIGHT = 600","pinned":false,"hidden":false,"mode":"ojs"},{"id":44,"value":"COLORS = ({ repellent: 'crimson', attractive: 'darkslategrey'})","pinned":false,"hidden":false,"mode":"ojs"},{"id":58,"value":"PARTICLE_RADIUS_RANGE = [2, 10]","pinned":false,"hidden":false,"mode":"ojs"},{"id":61,"value":"ACCELERATION_K = 0.3;","pinned":false,"hidden":false,"mode":"ojs"},{"id":12,"value":"**Dependencies**","pinned":false,"hidden":false,"mode":"md"},{"id":68,"value":"d3ForcePod = require('d3-force-pod@1.0.3')","pinned":false,"hidden":false,"mode":"ojs"},{"id":88,"value":"d3 = require('d3-force-bounce', 'd3-force-magnetic')","pinned":false,"hidden":false,"mode":"ojs"},{"id":20,"value":"import {slider} from \"@jashkenas/inputs\"","pinned":false,"hidden":false,"mode":"ojs"}],"files":"$W30","stdlib":"1","titling":"auto"}