imslinearmisc Module Reference

Functions/Subroutines
subroutine, public	ims_misc_thomas (n, tl, td, tu, b, x, w)
	Tridiagonal solve using the Thomas algorithm. More...

Function/Subroutine Documentation

ims_misc_thomas()

subroutine, public imslinearmisc::ims_misc_thomas	(	integer(i4b), intent(in)	n,
		real(dp), dimension(n), intent(in)	tl,
		real(dp), dimension(n), intent(in)	td,
		real(dp), dimension(n), intent(in)	tu,
		real(dp), dimension(n), intent(in)	b,
		real(dp), dimension(n), intent(inout)	x,
		real(dp), dimension(n), intent(inout)	w
	)

Subroutine to solve tridiagonal linear equations using the Thomas algorithm.

Parameters

[in]	n	number of matrix rows
[in]	tl	lower matrix terms
[in]	td	diagonal matrix terms
[in]	tu	upper matrix terms
[in]	b	right-hand side vector
[in,out]	x	solution vector
[in,out]	w	work vector

Definition at line 17 of file ImsLinearMisc.f90.

    implicit none
    ! -- dummy variables
    integer(I4B), intent(in) :: n !< number of matrix rows
    real(DP), dimension(n), intent(in) :: tl !< lower matrix terms
    real(DP), dimension(n), intent(in) :: td !< diagonal matrix terms
    real(DP), dimension(n), intent(in) :: tu !< upper matrix terms
    real(DP), dimension(n), intent(in) :: b !< right-hand side vector
    real(DP), dimension(n), intent(inout) :: x !< solution vector
    real(DP), dimension(n), intent(inout) :: w !< work vector
    ! -- local variables
    integer(I4B) :: j
    real(DP) :: bet
    real(DP) :: beti
    !
    ! -- initialize variables
    w(1) = dzero
    bet = td(1)
    beti = done / bet
    x(1) = b(1) * beti
    !
    ! -- decomposition and forward substitution
    do j = 2, n
      w(j) = tu(j - 1) * beti
      bet = td(j) - tl(j) * w(j)
      beti = done / bet
      x(j) = (b(j) - tl(j) * x(j - 1)) * beti
    end do
    !
    ! -- backsubstitution
    do j = n - 1, 1, -1
      x(j) = x(j) - w(j + 1) * x(j + 1)
    end do
    ! -- return
    return

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