*DECK PJAC
      SUBROUTINE PJAC (NEQ, Y, YH, NYH, EWT, FTEM, SAVF, WM, IWM, F,
     +   JAC, RPAR, IPAR)
C***BEGIN PROLOGUE  PJAC
C***SUBSIDIARY
C***PURPOSE  Subsidiary to DEBDF
C***LIBRARY   SLATEC
C***TYPE      SINGLE PRECISION (PJAC-S, DPJAC-D)
C***AUTHOR  Watts, H. A., (SNLA)
C***DESCRIPTION
C
C   PJAC sets up the iteration matrix (involving the Jacobian) for the
C   integration package DEBDF.
C
C***SEE ALSO  DEBDF
C***ROUTINES CALLED  SGBFA, SGEFA, VNWRMS
C***COMMON BLOCKS    DEBDF1
C***REVISION HISTORY  (YYMMDD)
C   800901  DATE WRITTEN
C   890531  Changed all specific intrinsics to generic.  (WRB)
C   891214  Prologue converted to Version 4.0 format.  (BAB)
C   900328  Added TYPE section.  (WRB)
C   910722  Updated AUTHOR section.  (ALS)
C   920422  Changed DIMENSION statement.  (WRB)
C***END PROLOGUE  PJAC
C
CLLL. OPTIMIZE
      INTEGER NEQ, NYH, IWM, I, I1, I2, IER, II, IOWND, IOWNS, J, J1,
     1   JJ, JSTART, KFLAG, L, LENP, MAXORD, MBA, MBAND, MEB1, MEBAND,
     2   METH, MITER, ML, ML3, MU, N, NFE, NJE, NQ, NQU, NST
      EXTERNAL F, JAC
      REAL Y, YH, EWT, FTEM, SAVF, WM,
     1   ROWND, ROWNS, EL0, H, HMIN, HMXI, HU, TN, UROUND,
     2   CON, DI, FAC, HL0, R, R0, SRUR, YI, YJ, YJJ, VNWRMS
      DIMENSION         Y(*), YH(NYH,*), EWT(*), FTEM(*), SAVF(*),
     1   WM(*), IWM(*), RPAR(*), IPAR(*)
      COMMON /DEBDF1/ ROWND, ROWNS(210),
     1   EL0, H, HMIN, HMXI, HU, TN, UROUND, IOWND(14), IOWNS(6),
     2   IER, JSTART, KFLAG, L, METH, MITER, MAXORD, N, NQ, NST, NFE,
     3   NJE, NQU
C-----------------------------------------------------------------------
C PJAC IS CALLED BY STOD  TO COMPUTE AND PROCESS THE MATRIX
C P = I - H*EL(1)*J , WHERE J IS AN APPROXIMATION TO THE JACOBIAN.
C HERE J IS COMPUTED BY THE USER-SUPPLIED ROUTINE JAC IF
C MITER = 1 OR 4, OR BY FINITE DIFFERENCING IF MITER = 2, 3, OR 5.
C IF MITER = 3, A DIAGONAL APPROXIMATION TO J IS USED.
C J IS STORED IN WM AND REPLACED BY P.  IF MITER .NE. 3, P IS THEN
C SUBJECTED TO LU DECOMPOSITION IN PREPARATION FOR LATER SOLUTION
C OF LINEAR SYSTEMS WITH P AS COEFFICIENT MATRIX. THIS IS DONE
C BY SGEFA IF MITER = 1 OR 2, AND BY SGBFA IF MITER = 4 OR 5.
C
C IN ADDITION TO VARIABLES DESCRIBED PREVIOUSLY, COMMUNICATION
C WITH PJAC USES THE FOLLOWING..
C Y    = ARRAY CONTAINING PREDICTED VALUES ON ENTRY.
C FTEM = WORK ARRAY OF LENGTH N (ACOR IN STOD ).
C SAVF = ARRAY CONTAINING F EVALUATED AT PREDICTED Y.
C WM   = REAL WORK SPACE FOR MATRICES.  ON OUTPUT IT CONTAINS THE
C        INVERSE DIAGONAL MATRIX IF MITER = 3 AND THE LU DECOMPOSITION
C        OF P IF MITER IS 1, 2 , 4, OR 5.
C        STORAGE OF MATRIX ELEMENTS STARTS AT WM(3).
C        WM ALSO CONTAINS THE FOLLOWING MATRIX-RELATED DATA..
C        WM(1) = SQRT(UROUND), USED IN NUMERICAL JACOBIAN INCREMENTS.
C        WM(2) = H*EL0, SAVED FOR LATER USE IF MITER = 3.
C IWM  = INTEGER WORK SPACE CONTAINING PIVOT INFORMATION, STARTING AT
C        IWM(21), IF MITER IS 1, 2, 4, OR 5.  IWM ALSO CONTAINS THE
C        BAND PARAMETERS ML = IWM(1) AND MU = IWM(2) IF MITER IS 4 OR 5.
C EL0  = EL(1) (INPUT).
C IER  = OUTPUT ERROR FLAG,  = 0 IF NO TROUBLE, .NE. 0 IF
C        P MATRIX FOUND TO BE SINGULAR.
C THIS ROUTINE ALSO USES THE COMMON VARIABLES EL0, H, TN, UROUND,
C MITER, N, NFE, AND NJE.
C-----------------------------------------------------------------------