public override string ToString() {
if (real == 0.0) return imag.ToString(System.Globalization.CultureInfo.InvariantCulture.NumberFormat) + "j";
else if (imag < 0.0) return string.Format(System.Globalization.CultureInfo.InvariantCulture.NumberFormat, "({0}{1}j)", real, imag);
else return string.Format(System.Globalization.CultureInfo.InvariantCulture.NumberFormat, "({0}+{1}j)", real, imag);
}