\section{Usage}The library includes both C and F90 bindings.  C methods and parameters begin with {\tt MF\_} (Modeling Framework) and F90 methods and parameters begin with {\tt MFM\_} (Modeling Framework Modules).\noindent {\bf Constraints}The library design imposes some constraints on the user:\begin{itemize}\item {\it No direct access of Fortran derived types.}  Attributesof Fortran derived types are private.\item{\it All types should be initialized.} In order to provide consistentargument checking and to inrease the overall robustness of the library,a user should call one of the {\tt ``Init''} routines before using thelibrary's Fortran derived types, or a {\tt ``Construct''} routine before using its C classes.\end{itemize}\noindent {\bf Error Handling}All C ({\tt MF\_*}) operations return an integer error code.  All F90 ({\tt MFM\_*}) operations have an optional integer return code argument.  Return codes are translated into error descriptions using the methods: \begin{verbatim}    void MF_ErrPrint(int rc)    subroutine MFM_ErrPrint(rc)      integer, intent(in) :: rc\end{verbatim}A return code of {\tt MF[M]\_SUCCESS} indicates that an operation executed without errors.The user can currently choose from two different error handlers.{\tt MF[M]\_ERR\_RETURN} will simply return from a routine in which an error is identified, without printing an error description.{\tt MF[M]\_ERR\_EXIT} will print a detailed error description includingfile, function name, and line number, and will then terminate execution(this is a simple exit, not an {\tt MPI\_ABORT}).  These handlers are set using the methods: \begin{verbatim}    void MF_ErrHandlerSetType(MF_ErrHandlerType type)    subroutine MFM_ErrHandlerSetType(type)    integer, intent(in) :: type\end{verbatim}The intent is to develop an MPI-like error handling system in whichusers can choose from a variety of handlers or supply their own.