DGESV_TEST
  Demonstrate the use of DGESV to solve a linear system
  using double precision real arithmetic.

  Coefficient matrix:

               1              -1               2              -1
               2              -2               3              -3
               1               1               1               0
               1              -1               4               3

  Right hand side:

              -8
             -20
              -2
               4

  Computed solution:

              -7
               3
               2
               2