#############################################################
# Building 'tdgesv' and sample output on the Cray J90.
#############################################################
charon% pwd; ls
/archive/utexas/ph/phas761/phy329/linsys/ex1

#############################################################
# Note that the 'blas' library is built-in on the Cray, so we 
# do not have to specify '-lblas' during the load phase. 
# Thus, the environment variable LIBBLAS (used in the Makefile)
# can either be unset, or set to nothing (the case here).
#############################################################
charon% printenv LIBBLAS

#############################################################
# Transfer the source code and the Makefile from einstein.
#############################################################
charon% ftp einstein.ph.utexas.edu
Connected to einstein.ph.utexas.edu.
                           .
                           .
                           .
Remote system type is UNIX.
Using binary mode to transfer files.
Name (einstein.ph.utexas.edu:phas761): phy329
331 Password required for phy329.
Password:
230 User phy329 logged in.

ftp> cd linsys/ex1
250 CWD command successful.

ftp> prompt
Interactive mode off.

ftp> mget Makefile *.f
                           .
                           .
                           .
ftp> quit
221 Goodbye.

#############################################################
# Using the 'Makefile', the source file is automatically 
# translated # to 'Cray-compatible' Fortran via the script 
# 'f77transcray'.  Note that 'f77transcray' handles the change 
# in name of the real*8 LAPACK routine from 'dgesv' to 'sgesv'.
#############################################################
charon% make
   f77transcray tdgesv.f
f77transcray: Translating tdgesv.f
   cf77 -g -c tdgesv.f
   cf77 -g -L/home/utexas/ph/phas761/lib \
        tdgesv.o -llapack  -o tdgesv

charon% cat tdgesv.f
c===========================================================
c     Test program for LAPACK "driver" routine 'dgesv' 
c     which computes the solution of a real system
c     of linear equations:  A x = b
c
c     This version uses fixed-size 2-d arrays.
c===========================================================
      program         tdgesv1

      implicit        none
c-----------------------------------------------------------
c     Maximum size of linear system.
c-----------------------------------------------------------
      integer         maxn
      parameter     ( maxn = 100 )

c-----------------------------------------------------------
c     Storage for arrays 
c-----------------------------------------------------------
      real            a(maxn,maxn),   
     &                b(maxn),        x(maxn)
      integer         ipiv(maxn)

      integer         i,              nrhs,      
     &                n,              info

c-----------------------------------------------------------
c     Set up sample 3 x 3 system ...
c-----------------------------------------------------------
      a(1,1) =  1.23e0
      a(1,2) =  0.24e0
      a(1,3) = -0.45e0

      a(2,1) = -0.43e0
      a(2,2) =  2.45e0
      a(2,3) =  0.78e0

      a(3,1) =  0.51e0
      a(3,2) = -0.68e0
      a(3,3) =  3.23e0

      b(1)   =  6.78e0
      b(2)   = -3.45e0
      b(3)   =  1.67e0

c-----------------------------------------------------------
c     ... and solve it.  Note that 'dgsev' is general 
c     enough to solve A x_i = b_i for multiple right-hand-
c     sides b_i.  Here we have only one right-hand-side.
c     Also note that the procedure performs the LU 
c     decomposition in place, thus destroying the 
c     input-matrix, it also overwrites the right-hand-side(s)
c     with the solution(s).  Finally, observe that we 
c     pass the "leading dimension" (maxn) of both 'a' and 
c     'b' to the routine.  This allows us to load array
c     elements in the main program as we have just done,
c     without running into troubles due to the fact that 
c     these elements ARE NOT all contiguous in memory.
c-----------------------------------------------------------
      n    = 3
      nrhs = 1

      call sgesv( n, nrhs, a, maxn, ipiv, b, maxn, info )

      if(      info .eq. 0 ) then
c-----------------------------------------------------------
c        Solution successful, write soln to stdout.       
c        Note the use of "implied-do-loop" to write a 
c        sequence of elements: the enclosing parenthesis 
c        around the  "loop" are required.
c-----------------------------------------------------------
         write(*,*) ( b(i) , i = 1 , n )
      else if( info .lt. 0 ) then
c-----------------------------------------------------------
c        Bad argument detected.
c-----------------------------------------------------------
         write(0,*) 'tdgesv1: Argument ', abs(info), 
     &              ' to sgesv() is invalid'
      else 
c-----------------------------------------------------------
c        Matrix is singular.
c-----------------------------------------------------------
         write(0,*) 'tdgesv1: sgesv() detected singular ',
     &              'matrix'
      end if
      

      stop

      end

#############################################################
# Run the test program.
#############################################################
charon% tdgesv

 5.426364412431667,  -0.325775376817397,  -0.4083508069894641

 STOP executed at line 88 in Fortran routine 'TDGESV1'
 CPU: 0.006s,  Wallclock: 0.043s,  1.7% of 8-CPU Machine
 Memory HWM: 232358, Stack HWM: 16509, Stack segment expansions: 0