# dbhin.f

          SUBROUTINE DBHIN (N, NELT, IA, JA, A, ISYM, SOLN, RHS, IUNIT, JOB)
    C***BEGIN PROLOGUE  DBHIN
    C***PURPOSE  Read a Sparse Linear System in the Boeing/Harwell Format.
    C            The matrix is read in and if the right hand side is also
    C            present in the input file then it too is read in.  The
    C            matrix is then modified to be in the SLAP Column format.
    C***LIBRARY   SLATEC (SLAP)
    C***CATEGORY  N1
    C***TYPE      DOUBLE PRECISION (SBHIN-S, DBHIN-D)
    C***KEYWORDS  LINEAR SYSTEM, MATRIX READ, SLAP SPARSE
    C***AUTHOR  Seager, Mark K., (LLNL)
    C             Lawrence Livermore National Laboratory
    C             PO BOX 808, L-60
    C             Livermore, CA 94550 (510) 423-3141
    C             seager@llnl.gov
    C***DESCRIPTION
    C
    C *Usage:
    C     INTEGER N, NELT, IA(NELT), JA(NELT), ISYM, IUNIT, JOB
    C     DOUBLE PRECISION A(NELT), SOLN(N), RHS(N)
    C
    C     CALL DBHIN( N, NELT, IA, JA, A, ISYM, SOLN, RHS, IUNIT, JOB )
    C
    C *Arguments:
    C N      :OUT      Integer
    C         Order of the Matrix.
    C NELT   :INOUT    Integer.
    C         On input NELT is the maximum number of non-zeros that
    C         can be stored in the IA, JA, A arrays.
    C         On output NELT is the number of non-zeros stored in A.
    C IA     :OUT      Integer IA(NELT).
    C JA     :OUT      Integer JA(NELT).
    C A      :OUT      Double Precision A(NELT).
    C         On output these arrays hold the matrix A in the SLAP
    C         Triad format.  See "Description", below.
    C ISYM   :OUT      Integer.
    C         Flag to indicate symmetric storage format.
    C         If ISYM=0, all non-zero entries of the matrix are stored.
    C         If ISYM=1, the matrix is symmetric, and only the lower
    C         triangle of the matrix is stored.
    C SOLN   :OUT      Double Precision SOLN(N).
    C         The solution to the linear system, if present.  This array
    C         is accessed if and only if JOB is set to read it in, see
    C         below.  If the user requests that SOLN be read in, but it is
    C         not in the file, then it is simply zeroed out.
    C RHS    :OUT      Double Precision RHS(N).
    C         The right hand side vector.  This array is accessed if and
    C         only if JOB is set to read it in, see below.
    C         If the user requests that RHS be read in, but it is not in
    C         the file, then it is simply zeroed out.
    C IUNIT  :IN       Integer.
    C         Fortran logical I/O device unit number to read the matrix
    C         from.  This unit must be connected in a system dependent
    C         fashion to a file, or you will get a nasty message
    C         from the Fortran I/O libraries.
    C JOB    :INOUT    Integer.
    C         Flag indicating what I/O operations to perform.
    C         On input JOB indicates what Input operations to try to
    C         perform.
    C         JOB = 0 => Read only the matrix.
    C         JOB = 1 => Read matrix and RHS (if present).
    C         JOB = 2 => Read matrix and SOLN (if present).
    C         JOB = 3 => Read matrix, RHS and SOLN (if present).
    C         On output JOB indicates what operations were actually
    C         performed.
    C         JOB = -3 => Unable to parse matrix "CODE" from input file
    C                     to determine if only the lower triangle of matrix
    C                     is stored.
    C         JOB = -2 => Number of non-zeros (NELT) too large.
    C         JOB = -1 => System size (N) too large.
    C         JOB =  0 => Read in only the matrix.
    C         JOB =  1 => Read in the matrix and RHS.
    C         JOB =  2 => Read in the matrix and SOLN.
    C         JOB =  3 => Read in the matrix, RHS and SOLN.
    C         JOB = 10 => Read in only the matrix *STRUCTURE*, but no
    C                     non-zero entries.  Hence, A(*) is not referenced
    C                     and has the return values the same as the input.
    C         JOB = 11 => Read in the matrix *STRUCTURE* and RHS.
    C         JOB = 12 => Read in the matrix *STRUCTURE* and SOLN.
    C         JOB = 13 => Read in the matrix *STRUCTURE*, RHS and SOLN.
    C
    C *Description:
    C       The format for the input is as follows.  The first line contains
    C       a title to identify the data file.  On the second line (5I4) are
    C       counters: NLINE, NPLS, NRILS, NNVLS, NRHSLS.
    C        NLINE  Number of data lines (after the header) in the file.
    C        NPLS   Number of lines for the Column Pointer data in the file.
    C        NRILS  Number of lines for the Row indices in the file.
    C        NNVLS  Number of lines for the Matrix elements in the file.
    C        NRHSLS Number of lines for the RHS in the file.
    C       The third line (A3,11X,4I4) contains a symmetry code and some
    C       additional counters: CODE, NROW, NCOL, NIND, NELE.
    C       On the fourth line (2A16,2A20) are formats to be used to read
    C       the following data: PNTFNT, RINFMT, NVLFMT, RHSFMT.
    C       Following that are the blocks of data in the order indicated.
    C
    C       =================== S L A P Triad format ===================
    C       This routine requires that the  matrix A be   stored in  the
    C       SLAP  Triad format.  In  this format only the non-zeros  are
    C       stored.  They may appear in  *ANY* order.  The user supplies
    C       three arrays of  length NELT, where  NELT is  the number  of
    C       non-zeros in the matrix: (IA(NELT), JA(NELT), A(NELT)).  For
    C       each non-zero the user puts the row and column index of that
    C       matrix element  in the IA and  JA arrays.  The  value of the
    C       non-zero  matrix  element is  placed   in  the corresponding
    C       location of the A array.   This is  an  extremely  easy data
    C       structure to generate.  On  the  other hand it   is  not too
    C       efficient on vector computers for  the iterative solution of
    C       linear systems.  Hence,   SLAP changes   this  input    data
    C       structure to the SLAP Column format  for  the iteration (but
    C       does not change it back).
    C
    C       Here is an example of the  SLAP Triad   storage format for a
    C       5x5 Matrix.  Recall that the entries may appear in any order.
    C
    C           5x5 Matrix      SLAP Triad format for 5x5 matrix on left.
    C                              1  2  3  4  5  6  7  8  9 10 11
    C       |11 12  0  0 15|   A: 51 12 11 33 15 53 55 22 35 44 21
    C       |21 22  0  0  0|  IA:  5  1  1  3  1  5  5  2  3  4  2
    C       | 0  0 33  0 35|  JA:  1  2  1  3  5  3  5  2  5  4  1
    C       | 0  0  0 44  0|
    C       |51  0 53  0 55|
    C
    C *Portability:
    C         You must make sure that IUNIT is a valid Fortran logical
    C         I/O device unit number and that the unit number has been
    C         associated with a file or the console.  This is a system
    C         dependent function.
    C
    C *Implementation note:
    C         SOLN is not read by this version.  It will simply be
    C         zeroed out if JOB = 2 or 3 and the returned value of
    C         JOB will indicate SOLN has not been read.
    C***REFERENCES  (NONE)
    C***ROUTINES CALLED  (NONE)
    C***REVISION HISTORY  (YYMMDD)
    C   881107  DATE WRITTEN
    C   881213  Previous REVISION DATE
    C   890915  Made changes requested at July 1989 CML Meeting.  (MKS)
    C   890922  Numerous changes to prologue to make closer to SLATEC
    C           standard.  (FNF)
    C   890929  Numerous changes to reduce SP/DP differences.  (FNF)
    C   910411  Prologue converted to Version 4.0 format.  (BAB)
    C   911122  Added loop to zero out RHS if user wants to read RHS, but
    C           it's not in the input file. (MKS)
    C   911125  Minor improvements to prologue.  (FNF)
    C   920511  Added complete declaration section.  (WRB)
    C   921007  Corrected description of input format.  (FNF)
    C   921208  Added Implementation Note and code to zero out SOLN.  (FNF)
    C   930701  Updated CATEGORY section.  (FNF, WRB)
    C***END PROLOGUE  DBHIN