zero, 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 computer code and data files described and made available on this web page are distributed under the GNU LGPL license.
zero is available in a C version and a C++ version and a FORTRAN90 version and a MATLAB version and a Python version. 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; R version by John Burkardt.