lambert-w-function/dist/index.js

An efficient JavaScript implementation for the Lambert W Function on the principial branch.

'use strict';
// src/index.ts
var E = Math.E, log = Math.log, exp = Math.exp;
var W0_LIMIT_POINT = -(1 / E);
function lambertW0_IaconoBoyd(x) {
    var is_x_log = arguments.length > 1 && arguments[1] !== void 0 ? arguments[1] : false;
    if (is_x_log) return lambertW0Log_xmodar(x);
    if (x >= 0) return lambertW0Log_xmodar(log(x));
    var xE = x * E;
    if (isNaN(x) || xE < -1) return NaN;
    var y = Math.pow(1 + xE, 0.5);
    var z = log(y + 1);
    var n = 1 + /* b= */ 1.1495613113577325 * y;
    var d = 1 + /* c= */ 0.4549574005654461 * z;
    var w = -1 + /* a= */ 2.036 * log(n / d);
    w *= log(xE / w) / (1 + w);
    w *= log(xE / w) / (1 + w);
    w *= log(xE / w) / (1 + w);
    return isNaN(w) ? xE < -0.5 ? -1 : x : w;
}
function lambertW0Log_xmodar(logX) {
    if (isNaN(logX)) return NaN;
    var logXE = +logX + 1;
    var logY = 0.5 * log1Exp(logXE);
    var logZ = log(log1Exp(logY));
    var logN = log1Exp(/* log(b)= */ 0.13938040121300527 + logY);
    var logD = log1Exp(/* log(c)= */ -0.7875514895451805 + logZ);
    var w = -1 + /* a= */ 2.036 * (logN - logD);
    w *= (logXE - log(w)) / (1 + w);
    w *= (logXE - log(w)) / (1 + w);
    w *= (logXE - log(w)) / (1 + w);
    return isNaN(w) ? logXE < 0 ? 0 : Infinity : w;
}
function log1Exp(x) {
    return x <= 0 ? Math.log1p(Math.exp(x)) : x + log1Exp(-x);
}
function lambertW0_SimpleIteration_LT_E(x) {
    var iterations = arguments.length > 1 && arguments[1] !== void 0 ? arguments[1] : 10;
    var y = 1;
    do {
        y = x / exp(y);
        iterations--;
    }while (iterations > 0);
    return y;
}
function lambertW0_SimpleIteration_GT_E(x) {
    var iterations = arguments.length > 1 && arguments[1] !== void 0 ? arguments[1] : 10;
    var y = 1;
    do {
        y = log(x) - log(y);
        iterations--;
    }while (iterations > 0);
    return y;
}
exports.W0_LIMIT_POINT = W0_LIMIT_POINT;
exports.lambertW0 = lambertW0_IaconoBoyd;
exports.lambertW0Log = lambertW0Log_xmodar;
exports.lambertW0Log_xmodar = lambertW0Log_xmodar;
exports.lambertW0_IaconoBoyd = lambertW0_IaconoBoyd;
exports.lambertW0_SimpleIteration_GT_E = lambertW0_SimpleIteration_GT_E;
exports.lambertW0_SimpleIteration_LT_E = lambertW0_SimpleIteration_LT_E;