Solve univariate function 'y = f(x)' using Brent's method.
First argument F is a function taking one numeric argument.
Return value of F has to be a real number.
Keyword argument Y is the function value. Default is zero.
Keyword argument INITIAL-VALUE is the initial value for the
function argument X.
Keyword arguments LOWER-BOUND and UPPER-BOUND specify the
interval bounds between which the root is searched. If any
one of these two arguments is omitted, the interval bounds
are determined automatically around INITIAL-VALUE.
Keyword argument MAX-ITER is the maximum number of iterations
to be performed. Default is 1000.
Keyword argument REL-TOL is the relative tolerance. Default
is machine precision.
Keyword argument ABS-TOL is the absolute tolerance. Default
is zero.
The iteration stops if half of the interval is less than
or equal to '2 * REL-TOL * |x| + ABS-TOL / 2'.
Primary value is the argument X for which 'y = f(x)' is true.
Secondary value is the number of iterations performed; nil
means that the algorithm did not converge within the given
number of iterations.