wsplintp.f90

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! Copyright (C) 2019 J. K. Dewhurst, S. Sharma and E. K. U. Gross.
! This file is distributed under the terms of the GNU General Public License.
! See the file COPYING for license details.
 
subroutine wsplintp(n,x,wp)
implicit none
! arguments
integer, intent(in) :: n
real(8), intent(in) :: x(n)
real(8), intent(out) :: wp(4,n)
! local variables
integer i
real(8) f(4),t1,t2
! external functions
real(8), external :: polynm
if (n < 4) then
  write(*,*)
  write(*,'("Error(wsplintp): n < 4 : ",I8)') n
  write(*,*)
  stop
end if
wp(:,1)=0.d0
f(1)=1.d0
f(2:)=0.d0
wp(1,2)=polynm(-1,4,x,f,x(2))
f(1)=0.d0
f(2)=1.d0
wp(2,2)=polynm(-1,4,x,f,x(2))
f(2)=0.d0
f(3)=1.d0
wp(3,2)=polynm(-1,4,x,f,x(2))
f(3)=0.d0
f(4)=1.d0
wp(4,2)=polynm(-1,4,x,f,x(2))
do i=3,n-1
  f(1)=1.d0
  f(2:)=0.d0
  t1=polynm(-1,4,x(i-2),f,x(i-1))
  t2=polynm(-1,4,x(i-2),f,x(i))
  wp(1,i)=t2-t1
  f(1)=0.d0
  f(2)=1.d0
  t1=polynm(-1,4,x(i-2),f,x(i-1))
  t2=polynm(-1,4,x(i-2),f,x(i))
  wp(2,i)=t2-t1
  f(2)=0.d0
  f(3)=1.d0
  t1=polynm(-1,4,x(i-2),f,x(i-1))
  t2=polynm(-1,4,x(i-2),f,x(i))
  wp(3,i)=t2-t1
  f(3)=0.d0
  f(4)=1.d0
  t1=polynm(-1,4,x(i-2),f,x(i-1))
  t2=polynm(-1,4,x(i-2),f,x(i))
  wp(4,i)=t2-t1
end do
f(1)=1.d0
f(2:)=0.d0
t1=polynm(-1,4,x(n-3),f,x(n-1))
t2=polynm(-1,4,x(n-3),f,x(n))
wp(1,n)=t2-t1
f(1)=0.d0
f(2)=1.d0
t1=polynm(-1,4,x(n-3),f,x(n-1))
t2=polynm(-1,4,x(n-3),f,x(n))
wp(2,n)=t2-t1
f(2)=0.d0
f(3)=1.d0
t1=polynm(-1,4,x(n-3),f,x(n-1))
t2=polynm(-1,4,x(n-3),f,x(n))
wp(3,n)=t2-t1
f(3)=0.d0
f(4)=1.d0
t1=polynm(-1,4,x(n-3),f,x(n-1))
t2=polynm(-1,4,x(n-3),f,x(n))
wp(4,n)=t2-t1
end subroutine