makeStateVec = (nodes) => {
return nodes.map(n => n.x)
.concat(nodes.map(n => n.y))
.concat(nodes.map(n => n.vx))
.concat(nodes.map(n => n.vy));
}
gravityField = (nodes, G) => {
// nodes are the nodes exhibiting gravitational forces, generally celestial bodies
// the s input below is supposed to be the values affecting each other, but since we're just doing fields,
// s will always be the initial state.
G = G || 1;
const n = nodes.length;
// Borrowed from https://observablehq.com/@mcmcclur/gravitation-and-the-n-body-problem
let x_accel = (x1, y1, s, j) => {
let m2 = nodes[j].m;
// In the n-body simulation, all the nodes are moving, but in this modified version
// nothing is moving, we're just grabbing the point in time acceleration.
// let x1 = s[i];
// let y1 = s[i + n];
let x2 = s[j];
let y2 = s[j + n];
return (m2 * (x2 - x1)) / ((x2 - x1) ** 2 + (y2 - y1) ** 2) ** (3 / 2);
};
let y_accel = (x1, y1, s, j) => {
let m2 = nodes[j].m;
// let x1 = s[i];
// let y1 = s[i + n];
let x2 = s[j];
let y2 = s[j + n];
return (m2 * (y2 - y1)) / ((x2 - x1) ** 2 + (y2 - y1) ** 2) ** (3 / 2);
};
let gr = (x, y, s) => {
return {
xpp: G*d3.sum(d3.range(nodes.length).map((i) => x_accel(x, y, s, i))),
ypp: G*d3.sum(d3.range(nodes.length).map((i) => y_accel(x, y, s, i))),
};
};
return gr
}
import {createStandardGrid, drawVector, addArrowHead, vectorAdd, vectorScale} from "@pcarleton/range-kutta-supporting-functions@309"
d3 = require('d3@7.3.0')
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