/// <summary>
/// 复数平方根
/// </summary>
public static Complex Sqrt(Complex c)
{
double x = c.Re, y = c.Im, mod = c.GetMod();
int sign = y < 0 ? -1 : 1;
double re = _halfOfSqrt2 * Math.Sqrt(mod + x),
im = _halfOfSqrt2 * sign * Math.Sqrt(mod - x);
return new Complex(re, im);
}