Fix exact coincidence with d3.forceCollide.

src/collide.js

@@ -1,5 +1,6 @@
 import constant from "./constant";
 import {quadtree} from "d3-quadtree";
+import {tau} from "./math";
 
 function x(d) {
   return d.x + d.vx;
@@ -51,7 +52,7 @@ export default function(radius) {
           l = x * x + y * y,
           r = radii[i] + radii[quad.data.index];
       if (l < r * r) {
-        l = (r - (l = Math.sqrt(l))) / l;
+        l = l ? (r - (l = Math.sqrt(l))) / l : (l = Math.random() * tau, x = Math.cos(l), y = Math.sin(l), r - 1);
         vx += x * l, vy += y * l;
       }
     }

src/link.js

@@ -1,7 +1,6 @@
 import {map} from "d3-collection";
 import constant from "./constant";
-
-var tau = 2 * Math.PI;
+import {tau} from "./math";
 
 function index(d, i) {
   return i;

src/manyBody.js

@@ -1,8 +1,7 @@
 import constant from "./constant";
 import {quadtree} from "d3-quadtree";
 import {x, y} from "./simulation";
-
-var tau = 2 * Math.PI;
+import {tau} from "./math";
 
 export default function() {
   var nodes,

src/math.js

@@ -0,0 +1,2 @@
+export var pi = Math.PI;
+export var tau = 2 * pi;

src/simulation.js

@@ -1,6 +1,7 @@
 import {dispatch} from "d3-dispatch";
 import {map} from "d3-collection";
 import {timer} from "d3-timer";
+import {pi} from "./math";
 
 export function x(d) {
   return d.x;
@@ -11,7 +12,7 @@ export function y(d) {
 }
 
 var initialRadius = 10,
-    initialAngle = Math.PI * (3 - Math.sqrt(5));
+    initialAngle = pi * (3 - Math.sqrt(5));
 
 export default function(nodes) {
   var simulation,