arclength Subroutine

private pure subroutine arclength(ntheta, nperiod, theta, gpar, arcl)

Uses

Given an initial theta and gradpar (=dtheta/dl) compute a new theta grid, returned in arcl, which has gradpar = dg/dl = constant.

Arguments

Type IntentOptional Attributes Name
integer, intent(in) :: ntheta
integer, intent(in) :: nperiod
real, intent(in), dimension(-ntgrid:) :: theta
real, intent(inout), dimension(-ntgrid:) :: gpar
real, intent(out), dimension(-ntgrid:) :: arcl

Contents

Source Code

arclength

Source Code

  pure subroutine arclength (ntheta, nperiod, theta, gpar, arcl)
    use constants, only: twopi, pi
    implicit none
    integer, intent (in) :: ntheta, nperiod
    real, dimension(-ntgrid:), intent (out) :: arcl
    real, dimension(-ntgrid:), intent (in) :: theta
    real, dimension(-ntgrid:), intent (in out) :: gpar
    integer :: nth, j
    real :: arcfac
    nth = ntheta / 2
    arcl(-nth) = 0.
    do j = -nth, nth-1
       arcl(j+1) = arcl(j) + 0.5 * (theta(j+1) - theta(j)) * (1. / gpar(j) + 1. / gpar(j+1))
    end do
    arcfac = 1. / arcl(nth)

    do j = -nth, nth
       arcl(j) = arcl(j) * twopi * arcfac - pi
    end do

    call periodic_copy(arcl, twopi, nperiod)
    gpar = twopi * arcfac
  end subroutine arclength