Source: chisquare.js

import { baseGenerator } from './base-generator'
import { normal } from './normal'
/**
 * Generates random numbers following a Chi-squared distribution.
 *
 * @param {number} k - Degrees of freedom (must be a positive integer).
 * @param {number|Array|null} [size=null] - The shape of the output:
 *   - If `null`, a single number is returned.
 *   - If a number, a 1D array of the specified size is returned.
 *   - If an array (e.g., [m, n]), a multidimensional array of the specified shape is returned.
 * @throws {Error} Throws an error if:
 *   - The `size` parameter is not a number, an array or null.
 *   - The degrees of freedom parameter k is not a positive integer.
 * @returns {number|Array} A random number or an array of random numbers from the Chi-squared distribution.
 */
export function chisquare(k, size = null) {
    if (!Number.isInteger(k) || k <= 0) {
        throw new Error("Degrees of freedom (k) must be a positive integer.")
    }

    const generateChi2 = () => {
        let sum = 0
        for (let i = 0; i < k; i++) {
            const z = normal()
            sum += z * z
        }
        return sum
    }

    return baseGenerator(generateChi2, size)
}