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-----------------------------------------------------------
      program         tdgesv

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

c-----------------------------------------------------------
c     Storage for arrays 
c-----------------------------------------------------------
      real*8          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) =  1.23d0
      a(1,2) =  0.24d0
      a(1,3) = -0.45d0

      a(2,1) = -0.43d0
      a(2,2) =  2.45d0
      a(2,3) =  0.78d0

      a(3,1) =  0.51d0
      a(3,2) = -0.68d0
      a(3,3) =  3.23d0

      b(1)   =  6.78d0
      b(2)   = -3.45d0
      b(3)   =  1.67d0

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 dgesv( 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,*) 'tdgesv: Argument ', abs(info), 
     &              ' to dgesv() is invalid'
      else 
c-----------------------------------------------------------
c        Matrix is singular.
c-----------------------------------------------------------
         write(0,*) 'tdgesv: dgesv() detected singular ',
     &              'matrix'
      end if
      

      stop

      end