The Complex class.
******************

   Class `Complex' is implemented in a way similar to that described by
Stroustrup. In keeping with libg++ conventions, the class is named
`Complex', not `complex'.  Complex arithmetic and relational operators
are provided (`+, -, *, /, +=, -=, *=, /=, ==, !=').  Attempted
division by (0, 0) triggers an exception.

   Complex numbers may be constructed and used in the following ways:

`Complex x;'
     Declares an uninitialized Complex.

`Complex x = 2; Complex y(2.0);'
     Set x and y to the Complex value (2.0, 0.0);

`Complex x(2, 3);'
     Sets x to the Complex value (2, 3);

`Complex u(x); Complex v = x;'
     Set u and v to the same value as x.

`double real(Complex& x);'
     returns the real part of x.

`double imag(Complex& x);'
     returns the imaginary part of x.

`double abs(Complex& x);'
     returns the magnitude of x.

`double norm(Complex& x);'
     returns the square of the magnitude of x.

`double arg(Complex& x);'
     returns the argument (amplitude) of x.

`Complex polar(double r, double t = 0.0);'
     returns a Complex with abs of r and arg of t.

`Complex conj(Complex& x);'
     returns the complex conjugate of x.

`Complex cos(Complex& x);'
     returns the complex cosine of x.

`Complex sin(Complex& x);'
     returns the complex sine of x.

`Complex cosh(Complex& x);'
     returns the complex hyperbolic cosine of x.

`Complex sinh(Complex& x);'
     returns the complex hyperbolic sine of x.

`Complex exp(Complex& x);'
     returns the exponential of x.

`Complex log(Complex& x);'
     returns the natural log of x.

`Complex pow(Complex& x, long p);'
     returns x raised to the p power.

`Complex pow(Complex& x, Complex& p);'
     returns x raised to the p power.

`Complex sqrt(Complex& x);'
     returns the square root of x.

`ostream << x;'
     prints x in the form (re, im).

`istream >> x;'
     reads x in the form (re, im), or just (re) or re in which case the
     imaginary part is set to zero.