This directory contains example programs for using the SimTKlapack library.  
The Makefile assumes  that the libSimTKlapack library was installed in
../../lib32_64.  and the SimTKlapack.h header file has been installed 
in ../include. 

You  will also have to set you _PATH_ environment variable at 
runtime to point to the installed location of the SimTKlapack library.

This directory contains two example programs for using SimTKlapack (dgesv.c and zgeev.c)
and one example program for checking the version information for SimTKlapack 
(check_lapack_version.c) 

The example programs show how C programs can call the Fortran interface for LAPACK
routines. 

The basic rules for C programs calling Fortran routines are:

1) Function names are in lower case and have an underscore appended to the name.
   For example, if a C program calls LAPACK's ZGEEV routine the call would be:
   zgeev_( ... ).

2) Fortran routines pass scalar arguments by reference. (except for character
   string "length" arguments that are normally hidden from FORTRAN programmers) 
   Therefore a C program needs to pass pointers to scalar arguments.

3) In Fortran 2-D arrays are stored in column major format meaning that 
   the matrix    A = [ 1.0 2.0 ]
                     [ 3.0 4.0 ]
  declared as a(2,2) would be stored in memory as 1.0, 3.0, 2.0, 4.0. 
  While a C 2-D array declared as a[2][2], would be stored in 
  row-major order as 1.0, 2.0, 3.0, 4.0.
  Therefore C programs may need to transpose 2D arrays before calling the 
  Fortran interface.

4) The lengths of character strings need to be passed as additional arguments
   which are added to the end of the parameter list.
   For example, LAPACK's ZGEEV  routine has two arguments which are character
   strings: JOBVL, JOBVR. 

   ZGEEV( JOBVL, JOBVR, N, A, LDA,  W,  VL,  LDVL,  VR,  LDVR,
                         WORK, LWORK, RWORK, INFO )


   A C program calling ZGEEV would need to add two additional
   arguments at the end of the parameter list which contain the lengths of JOBVL, JOBVR 
   arguments:

   char *jobvl = "N"; 
   char *jobvr = "V";
   int  len_jobvl = 1;  /* length of jobvl */
   int  len_jobvr = 1;  /* length of jobvr */
     .
     .
     .

   zgeev_( jobvl, jobvr, &n, a, &lda, w, vl, &ldvl, vr, &ldvr, work, &lwork, rwork, &info
           len_jobvl, len_jobvr);
           ^^^^^^^^   ^^^^^^^^
          additional arguments