program porte

  implicit none

  real :: x,L,C0,C1,xd,xf
  real :: H
  real :: C_init

  call recup_donnees(L,C0,C1,xd,xf)

  x = 0.
  print*, "x, C_init= ",x,C_init(x,L,C0,C1,xd,xf)
  x = (xd+xf)/2.
  print*, "x, C_init= ",x,C_init(x,L,C0,C1,xd,xf)
  x = L
  print*, "x, C_init= ",x,C_init(x,L,C0,C1,xd,xf)

end program porte


!------------
function H(x)

  implicit none
  real, intent(in) :: x
  real :: H

  if (x<0) then
          H = 0.
  else
          H = 1.
  end if

end function H


!-------------------------------
function C_init(x,L,C0,C1,xd,xf)

  implicit none
  real, intent(in) :: x,L,C0,C1,xd,xf
  real :: H
  real :: C_init

  C_init = C0 + (C1-C0)*(H(x-xd)-H(x-xf))

end function C_init


!--------------------------------------
subroutine recup_donnees(L,C0,C1,xd,xf)

        implicit none
        real, intent(out) :: L,C0,C1,xd,xf

        print*, "Donner la valeur de L:"
        read*, L
        print*, "Donner la valeur de C0:"
        read*, C0
        print*, "Donner la valeur de C1:"
        read*, C1
        print*, "Donner la valeur de xd:"
        read*, xd
        print*, "Donner la valeur de xf:"
        read*, xf

end subroutine recup_donnees