stheta_sq.f90

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! Copyright (C) 2008 J. K. Dewhurst, S. Sharma and C. Ambrosch-Draxl.
! This file is distributed under the terms of the GNU Lesser General Public
! License. See the file COPYING for license details.

!BOP
! !ROUTINE: stheta_sq
! !INTERFACE:
elemental real(8) function stheta_sq(x)
! !INPUT/OUTPUT PARAMETERS:
!   x : real argument (in,real)
! !DESCRIPTION:
!   Returns the Heaviside step function corresponding to the square-wave pulse
!   approximation to the Dirac delta function
!   $$ \tilde\Theta(x)=\left\{\begin{array}{ll}
!    0 & \quad x \le -1/2 \\
!    x+1/2 & \quad -1/2 < x < 1/2 \\
!    1 & \quad x\ge 1 \end{array}\right. $$
!
! !REVISION HISTORY:
!   Created July 2008 (JKD)
!EOP
!BOC
implicit none
! arguments
real(8), intent(in) :: x
if (x <= -0.5d0) then
  stheta_sq=0.d0
  return
end if
if (x < 0.5d0) then
  stheta_sq=x+0.5d0
else
  stheta_sq=1.d0
end if
end function
!EOC