Hi all !! I am a summer trainee and am currently making (modifying: I am changing the way the program takes input) a program in Fortran, and my math is a little shaky. What I have is an input file with 3 parameters in it for the equation (which is the equation for calculating torsional potential): K (1+cos(nQ-phi)) The parameters given to me are: K, n and phi. Now the program takes 7 parameters for this equation which are the prefactors for the corresponding power series (it does it that way because calculating double differential is easier then). So, I have to convert the given 3 parameters to the 7 parameters that the programs wants. How do I do that? I looked at the taylor series expansion on wikipedia, but I am not sure what I should expand this against. Is power series = maclaurin series? So I have to expand this around a=0? Thanks !!