zero_brent, an R code which finds a zero of a scalar function of a scalar variable, by Richard Brent.
The method does not derivatives, and does not assume that the function is differentiable.
The information on this web page is distributed under the MIT license.
zero_brent is available in a C version and a C++ version and a Fortran77 version and a Fortran90 version and a MATLAB version and an Octave version and a Python version and an R version.
newton, an R code which seeks a root of a single nonlinear function using the Newton method.
Original Fortran77 version by Richard Brent; This version by John Burkardt.