proj4js/lib/common/imlfn.js

module.exports = function(ml, e0, e1, e2, e3) {
  var phi;
  var dphi;

  phi = ml / e0;
  for (var i = 0; i < 15; i++) {
    dphi = (ml - (e0 * phi - e1 * Math.sin(2 * phi) + e2 * Math.sin(4 * phi) - e3 * Math.sin(6 * phi))) / (e0 - 2 * e1 * Math.cos(2 * phi) + 4 * e2 * Math.cos(4 * phi) - 6 * e3 * Math.cos(6 * phi));
    phi += dphi;
    if (Math.abs(dphi) <= 0.0000000001) {
      return phi;
    }
  }

  //..reportError("IMLFN-CONV:Latitude failed to converge after 15 iterations");
  return NaN;
};