/**
 * Barnes-Hut octree for n-body repulsion.
 *
 * @description
 * Every node in a force layout repels every other one, which is O(n²): at five
 * thousand nodes that is twenty-five million pairs per tick, and the layout
 * simply stops running. Barnes-Hut groups distant nodes into their centre of
 * mass and treats each group as one body, bringing a tick to O(n log n).
 *
 * `theta` is the accuracy dial: a cell is treated as a single body when its
 * width divided by the distance to it is below `theta`. Zero is exact and slow;
 * larger values are faster and coarser. 0.8 is the usual compromise and is what
 * makes thousands of nodes interactive.
 */
export interface OctreeBody {
    x: number;
    y: number;
    z: number;
    /** Repulsion weight. Defaults to 1 per body. */
    mass?: number;
}
export declare class Octree {
    private root;
    constructor(bodies: OctreeBody[]);
    private insert;
    /**
     * Accumulates the repulsion acting on one body.
     *
     * @param strength - Coulomb constant. Negative values attract.
     * @param theta - Accuracy dial; see the module description.
     * @param out - Mutated in place, so a tick allocates nothing per body.
     */
    accumulate(body: OctreeBody, strength: number, theta: number, out: {
        fx: number;
        fy: number;
        fz: number;
    }, 
    /**
     * Floor on the separation used in the inverse-square term.
     *
     * Without it, two nearly coincident nodes divide by an almost-zero distance
     * and produce a force large enough to fling the whole graph to infinity on
     * the first tick. This is the single most important guard in the layout.
     */
    minDistance?: number): void;
    private walk;
}