function for the first derivative
function of the second derivative
Merge pull request #7 from JackStat/master

merge
Update df.R

already exists a df function in R, renaming it to d1f. Will also be updating functions that require the df function
Rename df.R to d1f.R
Update newton.raph.R

updated df to d1f
Merge pull request #11 from dcaff/master

merge