thi-ng/umbrella

import { lowDiscrepancy } from "./lowdisc.js";

/**
 * Iterator yielding 1D Halton sequence for given `base` (preferably a prime).
 *
 * @remarks
 * Ported from Python version at: https://en.wikipedia.org/wiki/Halton_sequence
 *
 * @param base -
 */
export function* halton(base: number) {
    let n = 0;
    let d = 1;
    let invB = 1 / base;
    while (true) {
        let x = d - n;
        if (x === 1) {
            n = 1;
            d *= base;
        } else {
            let y = (d * invB) | 0;
            while (x <= y) {
                y = (y * invB) | 0;
            }
            n = (base + 1) * y - x;
        }
        yield n / d;
    }
}

/**
 * n-dimensional version of {@link halton}. Takes a vector of `bases` (one per
 * dimension) and yields iterator of nD points. If `offset` > 0, the stated
 * number of initial iterations will be skipped.
 *
 * @param bases -
 * @param offset -
 */
export const haltonND = (bases: number[], offset = 0) =>
    lowDiscrepancy(bases.map(halton), offset);