Hello, I am trying to write a Fortran subroutine to solve non-linear equations (given by external function fnxname) using Newton's method, where the derivative is given by finite difference calculation. How may I use the function in the program. Suppose the desired function name is given by a string "fnxname", I cannot write fnxname(x), can I? In MATLAB, I may write eval(cat('fnxname','(x)')) or something like that. Is there a similar command in Fortran? Replies would be much appreciated. Thank you very much.