PROGRAM matrix
  USE constants
  USE F90library
  IMPLICIT NONE
  !      The definition of the matrix, using dynamic allocation
  REAL(DP), ALLOCATABLE, DIMENSION(:,:) :: a, ainv, unity
  !      the determinant
  REAL(DP) :: d
  !      The size of the matrix
  INTEGER :: n
  ....
  !      Allocate now place in heap for a
  ALLOCATE ( a(n,n), ainv(n,n), unity(n,n) )