/// <summary>
/// This function returns the complex arctangent of the complex number
/// a, arctan(a)}. The branch cuts are on the imaginary axis,
/// below -i and above i .
/// </summary>
/// <param name="a">The function argument.</param>
/// <returns>The complex arctangent of the complex number a.</returns>
public static Complex Atan(Complex a)
{
double R = a.Re, I = a.Im;
Complex z;
if (I == 0)
{
z = new Complex(Math.Atan(R), 0);
}
else
{
/* FIXME: This is a naive implementation which does not fully
* take into account cancellation errors, overflow, underflow
* etc. It would benefit from the Hull et al treatment. */
double r = hypot(R, I);
double imag;
double u = 2 * I / (1 + r * r);
/* FIXME: the following cross-over should be optimized but 0.1
* seems to work ok */
if (Math.Abs(u) < 0.1)
{
imag = 0.25 * (RMath.Log1p(u) - RMath.Log1p(-u));
}
else
{
double A = hypot(R, I + 1);
double B = hypot(R, I - 1);
imag = 0.5 * Math.Log(A / B);
}
if (R == 0)
{
if (I > 1)
{
z = new Complex(M_PI_2, imag);
}
else if (I < -1)
{
z = new Complex(-M_PI_2, imag);
}
else
{
z = new Complex(0, imag);
}
}
else
{
z = new Complex(0.5 * Math.Atan2(2 * R, ((1 + r) * (1 - r))), imag);
}
}
return(z);
}
/// <summary>
/// Return log |z|.
/// </summary>
/// <param name="z">The complex function argument.</param>
/// <returns>log |z|, i.e. the natural logarithm of the absolute value of z.</returns>
public static double LogAbs(Complex z)
{
double xabs = Math.Abs(z.Re);
double yabs = Math.Abs(z.Im);
double max, u;
if (xabs >= yabs)
{
max = xabs;
u = yabs / xabs;
}
else
{
max = yabs;
u = xabs / yabs;
}
// Handle underflow when u is close to 0
return(Math.Log(max) + 0.5 * RMath.Log1p(u * u));
}
/// <summary>
/// This function returns the complex arcsine of the complex number a,
/// arcsin(a)}. The branch cuts are on the real axis, less than -1
/// and greater than 1.
/// </summary>
/// <param name="a">The function argument.</param>
/// <returns>the complex arcsine of the complex number a.</returns>
public static Complex Asin(Complex a)
{
double R = a.Re, I = a.Im;
Complex z;
if (I == 0)
{
z = Asin(R);
}
else
{
double x = Math.Abs(R), y = Math.Abs(I);
double r = hypot(x + 1, y), s = hypot(x - 1, y);
double A = 0.5 * (r + s);
double B = x / A;
double y2 = y * y;
double real, imag;
const double A_crossover = 1.5, B_crossover = 0.6417;
if (B <= B_crossover)
{
real = Math.Asin(B);
}
else
{
if (x <= 1)
{
double D = 0.5 * (A + x) * (y2 / (r + x + 1) + (s + (1 - x)));
real = Math.Atan(x / Math.Sqrt(D));
}
else
{
double Apx = A + x;
double D = 0.5 * (Apx / (r + x + 1) + Apx / (s + (x - 1)));
real = Math.Atan(x / (y * Math.Sqrt(D)));
}
}
if (A <= A_crossover)
{
double Am1;
if (x < 1)
{
Am1 = 0.5 * (y2 / (r + (x + 1)) + y2 / (s + (1 - x)));
}
else
{
Am1 = 0.5 * (y2 / (r + (x + 1)) + (s + (x - 1)));
}
imag = RMath.Log1p(Am1 + Math.Sqrt(Am1 * (A + 1)));
}
else
{
imag = Math.Log(A + Math.Sqrt(A * A - 1));
}
z = new Complex((R >= 0) ? real : -real, (I >= 0) ? imag : -imag);
}
return(z);
}
