My question may be elementary, but it is quite essential as I am getting confused.Here I am supposed to solve the following equation:$Ax=B$From my understanding I have options of using either direct solvers or iterative solvers. I have tried using iterative solver GMRES(It is quite simple in terms of implementation on Fortran 90) but now I would like to use a direct solver for certain reasons and from resources and reviews I have shortlisted three of them: UMFPACK SUPERLU  MUMPS  I think the first two are developed using C and could be called from Fortran 90; The third one is in Fortran 90.Now, my question is how do I implement this or call function from my Fortran 90 code, ie. is there a reliable procedure to install or call the libraries? There looks to be tons of literature beyond my scope of understanding. To simplify, I have a sparse symmetric matrix $A$ , stored in skyline format and rhs vector $B$, how do I calculate $x$ using one of the direct sparse solvers in Fortran 90? 
Implementation of a direct solver in Fortran 90?
linear solver;sparse