program gaussian

            implicit none
            integer i, j, k
            character(1) c

    open(unit=100, file='energyDensity.vtk',
 1        form="unformatted",access="stream")
    write(100) '# vtk DataFile Version 3.0', new_line(c)
    write(100) 'First time trying vtk import n', new_line(c)
    write(100) 'BINARY', new_line(c)
    write(100) 'DATASET STRUCTURED_POINTS', new_line(c)
    write(100) 'DIMENSIONS 101 101 101', new_line(c)
    write(100) 'ORIGIN 0 0 0', new_line(c)
    write(100) 'SPACING 1 1 1', new_line(c)
    write(100) 'POINT_DATA 1030301', new_line(c)
    write(100) 'SCALARS volume_scalars double 1', new_line(c)
    write(100) 'LOOKUP_TABLE default', new_line(c)


            do k = -50,50
            do j = -50,50
            do i = -50,50

            write(100) 50.*exp(float((-(i*i+j*j+k*k))/25))

            enddo
            enddo
            enddo
    close(100)

endprogram

vtkNew<vtkStructuredPointsReader> reader;
  reader->SetFileName (argv[1]);
  reader->Update();

program gaussian

   use iso_fortran_env

            implicit none
            integer i, j, k
            character(1) c

    open(unit=100, file='energyDensity.vtk', &
         form="unformatted",access="stream")
    write(100) '# vtk DataFile Version 3.0', new_line(c)
    write(100) 'First time trying vtk import n', new_line(c)
    write(100) 'BINARY', new_line(c)
    write(100) 'DATASET STRUCTURED_POINTS', new_line(c)
    write(100) 'DIMENSIONS 101 101 101', new_line(c)
    write(100) 'ORIGIN 0 0 0', new_line(c)
    write(100) 'SPACING 1 1 1', new_line(c)
    write(100) 'POINT_DATA 1030301', new_line(c)
    write(100) 'SCALARS volume_scalars double 1', new_line(c)
    write(100) 'LOOKUP_TABLE default', new_line(c)


            do k = -50,50
            do j = -50,50
            do i = -50,50

            write(100) SwapB64(exp(real((-(i*i+j*j+k*k)), real64) / 25))

            enddo
            enddo
            enddo
    close(100)
contains

    elemental function SwapB64(x) result(res)
      real(real64) :: res
      real(real64),intent(in) :: x
      character(8) :: bytes
      integer(int64) :: t
      real(real64) :: rbytes, rt
      equivalence (rbytes, bytes)
      equivalence (t, rt)

      rbytes = x

      t = ichar(bytes(8:8),int64)

      t = ior( ishftc(ichar(bytes(7:7),int64),8),  t )

      t = ior( ishftc(ichar(bytes(6:6),int64),16), t )

      t = ior( ishftc(ichar(bytes(5:5),int64),24), t )

      t = ior( ishftc(ichar(bytes(4:4),int64),32), t )

      t = ior( ishftc(ichar(bytes(3:3),int64),40), t )

      t = ior( ishftc(ichar(bytes(2:2),int64),48), t )

      t = ior( ishftc(ichar(bytes(1:1),int64),56), t )

      res = rt

    end function
endprogram