C    Copyright(C) 1999-2020 National Technology & Engineering Solutions
C    of Sandia, LLC (NTESS).  Under the terms of Contract DE-NA0003525 with
C    NTESS, the U.S. Government retains certain rights in this software.
C
C    See packages/seacas/LICENSE for details

      SUBROUTINE ADD2CN (MXND, MLN, XN, YN, NUID, LXK, KXL, NXL, LXN,
     &   ANGLE, BNSIZE, LNODES, NNN, KKK, LLL, NNNOLD, LLLOLD, NLOOP,
     &   I1, IAVAIL, NAVAIL, GRAPH, VIDEO, SIZEIT, NOROOM, ERR, XNOLD,
     &   YNOLD, NXKOLD, LINKEG, LISTEG, BMESUR, MLINK, NPNOLD, NPEOLD,
     &   NNXK, REMESH, REXMIN, REXMAX, REYMIN, REYMAX, IDIVIS, SIZMIN,
     &   EMAX, EMIN)
C***********************************************************************

C  SUBROUTINE ADD2CN = ADDS TWO CENTER NODES IN THE MIDDLE OF 6 CLOSING

C***********************************************************************

      DIMENSION XN (MXND), YN (MXND), NUID (MXND)
      DIMENSION LXK (4, MXND), KXL (2, 3*MXND)
      DIMENSION NXL (2, 3*MXND), LXN (4, MXND)
      DIMENSION ANGLE (MXND), LNODES (MLN, MXND), BNSIZE (2, MXND)

      DIMENSION XNOLD(NPNOLD), YNOLD(NPNOLD)
      DIMENSION NXKOLD(NNXK, NPEOLD)
      DIMENSION LINKEG(2, MLINK), LISTEG(4 * NPEOLD), BMESUR(NPNOLD)

      LOGICAL GRAPH, VIDEO, ERR, AMBIG, SIZEIT, NOROOM

      ERR = .FALSE.
      AMBIG = .FALSE.

      I2 = LNODES (3, I1)
      I3 = LNODES (3, I2)
      I4 = LNODES (3, I3)
      I5 = LNODES (3, I4)
      I6 = LNODES (3, I5)

C  CALCULATE THE TWO NEW CENTER LOCATIONS

      X16 = ( XN(I1) + XN(I6) ) * .5
      X45 = ( XN(I4) + XN(I5) ) * .5
      XMID = (X16 + X45) * .5
      XNEW1 = (X16 + XMID) * .5
      XNEW2 = (X45 + XMID) * .5

      Y16 = ( YN(I1) + YN(I6) ) * .5
      Y45 = ( YN(I4) + YN(I5) ) * .5
      YMID = (Y16 + Y45) * .5
      YNEW1 = (Y16 + YMID) * .5
      YNEW2 = (Y45 + YMID) * .5

      ZERO = 0.

      CALL ADDNOD (MXND, MLN, XN, YN, LXK, KXL, NXL, LXN, ANGLE, BNSIZE,
     &   LNODES, XNEW1, YNEW1, ZERO, NNN, KKK, LLL, I6, I1, I2,
     &   AMBIG, IDUM, SIZEIT, ERR, NOROOM, XNOLD, YNOLD, NXKOLD,
     &   LINKEG, LISTEG, BMESUR, MLINK, NPNOLD, NPEOLD, NNXK, REMESH,
     &   REXMIN, REXMAX, REYMIN, REYMAX, IDIVIS, SIZMIN, EMAX, EMIN)
      IF ((ERR) .OR. (NOROOM)) GOTO 100
      INEW = NNN
      LNODES (4, INEW) = - 2
      IF ((GRAPH) .OR. (VIDEO)) THEN
         CALL D2NODE (MXND, XN, YN, I6, INEW)
         CALL D2NODE (MXND, XN, YN, I2, INEW)
         CALL SFLUSH
         IF (VIDEO) CALL SNAPIT (1)
      ENDIF
      CALL ADDNOD (MXND, MLN, XN, YN, LXK, KXL, NXL, LXN, ANGLE, BNSIZE,
     &   LNODES, XNEW2, YNEW2, ZERO, NNN, KKK, LLL, INEW, I2, I3,
     &   AMBIG, IDUM, SIZEIT, ERR, NOROOM, XNOLD, YNOLD, NXKOLD,
     &   LINKEG, LISTEG, BMESUR, MLINK, NPNOLD, NPEOLD, NNXK, REMESH,
     &   REXMIN, REXMAX, REYMIN, REYMAX, IDIVIS, SIZMIN, EMAX, EMIN)
      IF ((ERR) .OR. (NOROOM)) GOTO 100
      JNEW = NNN
      LNODES (4, JNEW) = - 2
      IF ((GRAPH) .OR. (VIDEO)) THEN
         CALL D2NODE (MXND, XN, YN, INEW, JNEW)
         CALL D2NODE (MXND, XN, YN, I3, JNEW)
         CALL SFLUSH
         IF (VIDEO) CALL SNAPIT (1)
      ENDIF
      CALL CONNOD (MXND, MLN, XN, YN, NUID, LXK, KXL, NXL, LXN, ANGLE,
     &   LNODES, NNN, KKK, LLL, NNNOLD, LLLOLD, JNEW, I3, I4, I5, IDUM,
     &   NLOOP, IAVAIL, NAVAIL, GRAPH, VIDEO, NOROOM, ERR)
      IF ((NOROOM) .OR. (ERR)) GOTO 100
      CALL CLOSE4 (MXND, MLN, LXK, KXL, NXL, LXN, LNODES,
     &   INEW, JNEW, I5, I6, KKK, ERR)

  100 CONTINUE

      RETURN

      END