! This file:
! http://ftp.aset.psu.edu/pub/ger/fortran/hdk/MatrixMultOperator.f90
!
! Example of how to create an operator using Fortran 90/95
! In this case .x. will be a matrix multiplication operator.
!
! by Michael Metcalf as posted at comp.lang.fortran
! with the function my_matmul rewritten by Jos R Bergervoet.
!
module mxmult

  interface operator(.x.)
     module procedure my_matmul
  end interface

  contains
    function my_matmul(x, y)
       real, dimension(:, :), intent(in)     :: x, y
       real, dimension(size(x,1), size(y,2)) :: my_matmul

       my_matmul = matmul(x, y)  ! matmul is F90 Intrinsic Procedure.
    end function

end module

program mxmdemo
! Demonstrate with a simple example
  use mxmult
  REAL , dimension(3,3) :: A,B,C,D,E

! Initialize right-hand matrices to constant values.
  A= 1. ; b=2. ; c = 3. ; E = 4.

  D=(A.x.B.x.C)+E

  do I=1,3
    print *, (D(I,J),J=1,3)
  end do
! Value of all elements of D are: 58.0

end