FIND_NODES.f90

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     SUBROUTINE find_nodes
       use data_declarations

       IMPLICIT NONE

       INTEGER :: num_matches    ! The number of nodes with matching XY coord values
                                 ! This should equal numscale_np and is used for verification
       INTEGER :: iteration      ! The number of iteration the subroutine has gone through
       INTEGER :: max_iterations ! The maximum number of iterations for the search algorithm
       INTEGER :: step           ! The step value for redifining the tolerances

       REAL*8 :: low_tol       ! The lower tolerance by which 'FIND_NODES' determines a match
       REAL*8 :: hi_tol        ! The upper tolerance by which 'FIND_NODES' determines a match

       ! Variable initializations
       low_tol = 99999.00000
       hi_tol = 100001.00000
       max_iterations = 5
       iteration = 1
       step = 5

       IF (numscale_ft .NE. numscale_bk) THEN
          WRITE(6,*) "ERROR:  The number of nodes on the front and back surfaces do not equal."
          WRITE(6,*) "Please check your mesh and try again."
          stop
       ENDIF

       WRITE(6,'(//A)') "Beginning search on sister nodes... This could take a while"

100    frontnode => first_front_node
       backnode => first_back_node
       num_matches = 0
       iteration = iteration + 1

       DO WHILE(associated(backnode%next))
          DO WHILE(associated(frontnode%next))

!             WRITE(6,*) "COORDS"
!             WRITE(6,*) "backnode", backnode%ID, backnode%coord(1:3)
!             WRITE(6,*) "frontnode", frontnode%ID, frontnode%coord(1:3)

!             WRITE(6,*) "DIVISION"
!             WRITE(6,*) backnode%coord(1)/frontnode%coord(1)
!             WRITE(6,*) backnode%coord(2)/frontnode%coord(2)

             ! If the 'X' coord is almost identical for both nodes THEN
             ! check the 'Y' coord value
             IF ((backnode%coord(1) .EQ. frontnode%coord(1)) .OR. &
                  ((backnode%coord(1)/frontnode%coord(1) .GT. low_tol/100000) .AND. &
                  (backnode%coord(1)/frontnode%coord(1) .LT. hi_tol/100000))) THEN
                ! IF the 'Y' coord is almost identical for both nodes THEN
                ! these nodes are sister nodes (a match is found)
                IF((backnode%coord(2) .EQ. frontnode%coord(2)) .OR. &
                     ((backnode%coord(2)/frontnode%coord(2) .GT. low_tol/100000) .AND. &
                     (backnode%coord(2)/frontnode%coord(2) .LT. hi_tol/100000))) THEN
                   backnode%sister => frontnode
                   frontnode%sister => backnode
                   num_matches = num_matches + 1
                ENDIF
             ENDIF
             ! proceed to the next node
             frontnode => frontnode%next
          ENDDO
          ! Once all the front nodes are cycled through, proceed to the next backnode
          ! and begin the search again
          backnode => backnode%next
          frontnode => first_front_node
       ENDDO



!!$       WRITE(6,*) "Writing node match information to '3Dnodematch.dat' file..."
!!$
!!$       OPEN(UNIT = 400, FILE = '3Dnodematch.dat', STATUS = 'UNKNOWN')
!!$
!!$       frontnode => first_front_node
!!$       backnode => first_back_node
!!$
!!$       WRITE(400,'(A8,3(6X,A1,5X),5X,A9,3(6X,A1,5X))') &
!!$            "BACKNODE", "X", "Y", "Z", "FRONTNODE", "X", "Y", "Z"
!!$
!!$       DO WHILE(associated(frontnode%next) .AND. associated(backnode%next))
!!$          WRITE(400,'(I8,3F12.8,6X,I8,3F12.8)') backnode%ID, backnode%coord(1:3), &
!!$                                      backnode%sister%ID, backnode%sister%coord(1:3)
!!$          frontnode => frontnode%next
!!$          backnode => backnode%next
!!$       END DO
!!$
!!$       CLOSE(400)



       WRITE(6,*) "Number of verified matches: ", num_matches
       WRITE(6,*) "Number of intended matches: ", numscale_np/2

       IF (iteration .LE. max_iterations) THEN
          IF (numscale_np/2 .NE. num_matches) THEN
             WRITE(6,*) "There was a failure in matching up the desired number of nodes."
             WRITE(6,*) "Redefining tolerances and starting iteration number ", iteration
             low_tol = low_tol - step
             hi_tol = hi_tol + step
             goto 100
             ELSE IF (numscale_np/2 .EQ. num_matches) THEN
                WRITE(6,*) "Number of matches confirmed.  Proceeding to next step."
          ENDIF
       ENDIF

     END SUBROUTINE find_nodes