Implementation for Brent's algorithm for minimizing a univariate function over an interval.
The code is based on a function in the stsm package.
BrentMethod(a = 0, b, fcn, tol = .Machine$double.eps^0.25)a list of containing the following elements:
fx the minimum value of the input function
x the argument that minimizes the function
iter number of iterations to converge
vx a vector that stores the arguments until convergence
lower limit for search
upper limit for search
function to minimize
tolerance level for convergence of the optimization procedure