[n,nelt,ia,ja,a,isym,dinv]=ssds(n,nelt,ia,ja,a,isym,dinv);

function [n,nelt,ia,ja,a,isym,dinv]=ssds(n,nelt,ia,ja,a,isym,dinv);
%***BEGIN PROLOGUE  SSDS
%***PURPOSE  Diagonal Scaling Preconditioner SLAP Set Up.
%            Routine to compute the inverse of the diagonal of a matrix
%            stored in the SLAP Column format.
%***LIBRARY   SLATEC (SLAP)
%***CATEGORY  D2E
%***TYPE      SINGLE PRECISION (SSDS-S, DSDS-D)
%***KEYWORDS  DIAGONAL, SLAP SPARSE
%***AUTHOR  Greenbaum, Anne, (Courant Institute)
%           Seager, Mark K., (LLNL)
%             Lawrence Livermore National Laboratory
%             PO BOX 808, L-60
%             Livermore, CA 94550 [phone]
%             [e-mail]
%***DESCRIPTION
%
% *Usage:
%     INTEGER N, NELT, IA(NELT), JA(NELT), ISYM
%     REAL    A(NELT), DINV(N)
%
%     CALL SSDS( N, NELT, IA, JA, A, ISYM, DINV )
%
% *Arguments:
% N      :IN       Integer.
%         Order of the Matrix.
% NELT   :IN       Integer.
%         Number of elements in arrays IA, JA, and A.
% IA     :INOUT    Integer IA(NELT).
% JA     :INOUT    Integer JA(NELT).
% A      :INOUT    Real A(NELT).
%         These arrays should hold the matrix A in the SLAP Column
%         format.  See 'Description', below.
% ISYM   :IN       Integer.
%         Flag to indicate symmetric storage format.
%         If ISYM=0, all non-zero entries of the matrix are stored.
%         If ISYM=1, the matrix is symmetric, and only the upper
%         or lower triangle of the matrix is stored.
% DINV   :OUT      Real DINV(N).
%         Upon return this array holds 1./DIAG(A).
%
% *Description
%       =================== S L A P Column format ==================
%       This routine  requires that  the matrix A  be stored in  the
%       SLAP Column format.  In this format the non-zeros are stored
%       counting down columns (except for  the diagonal entry, which
%       must appear first in each  'column')  and are stored  in the
%       real array A.  In other words, for each column in the matrix
%       put the diagonal entry in A.  Then put in the other non-zero
%       elements going down   the  column (except  the diagonal)  in
%       order.  The IA array holds the row  index for each non-zero.
%       The JA array holds the offsets into the IA, A arrays for the
%       beginning of   each    column.    That  is,    IA(JA(ICOL)),
%       A(JA(ICOL)) points to the beginning of the ICOL-th column in
%       IA and  A.  IA(JA(ICOL+1)-1),  A(JA(ICOL+1)-1) points to the
%       end  of   the ICOL-th  column.  Note   that  we  always have
%       JA(N+1) = NELT+1, where  N  is the number of columns in  the
%       matrix and  NELT   is the number of non-zeros in the matrix.
%
%       Here is an example of the  SLAP Column  storage format for a
%       5x5 Matrix (in the A and IA arrays '|'  denotes the end of a
%       column):
%
%           5x5 Matrix      SLAP Column format for 5x5 matrix on left.
%                              1  2  3    4  5    6  7    8    9 10 11
%       |11 12  0  0 15|   A: 11 21 51 | 22 12 | 33 53 | 44 | 55 15 35
%       |21 22  0  0  0|  IA:  1  2  5 |  2  1 |  3  5 |  4 |  5  1  3
%       | 0  0 33  0 35|  JA:  1  4  6    8  9   12
%       | 0  0  0 44  0|
%       |51  0 53  0 55|
%
%       With the SLAP  format  all  of  the   'inner  loops' of this
%       routine should vectorize  on  machines with hardware support
%       for vector   gather/scatter  operations.  Your compiler  may
%       require a compiler directive to  convince it that  there are
%       no  implicit  vector  dependencies.  Compiler directives for
%       the Alliant    FX/Fortran and CRI   CFT/CFT77 compilers  are
%       supplied with the standard SLAP distribution.
%
%
% *Cautions:
%       This routine assumes that the diagonal of A is all  non-zero
%       and that the operation DINV = 1.0/DIAG(A) will not underflow
%       or overflow.    This  is done so that the  loop  vectorizes.
%       Matrices  with zero or near zero or very  large entries will
%       have numerical difficulties  and  must  be fixed before this
%       routine is called.
%***REFERENCES  (NONE)
%***ROUTINES CALLED  (NONE)
%***REVISION HISTORY  (YYMMDD)
%   871119  DATE WRITTEN
%   881213  Previous REVISION DATE
%   890915  Made changes requested at July 1989 CML Meeting.  (MKS)
%   890922  Numerous changes to prologue to make closer to SLATEC
%           standard.  (FNF)
%   890929  Numerous changes to reduce SP/DP differences.  (FNF)
%   910411  Prologue converted to Version 4.0 format.  (BAB)
%   920511  Added complete declaration section.  (WRB)
%   930701  Updated CATEGORY section.  (FNF, WRB)
%***end PROLOGUE  SSDS
%     .. Scalar Arguments ..
%     .. Array Arguments ..
%     .. Local Scalars ..
persistent icol ; 

if isempty(icol), icol=0; end;
%***FIRST EXECUTABLE STATEMENT  SSDS
%
%         Assume the Diagonal elements are the first in each column.
%         This loop should *VECTORIZE*.  If it does not you may have
%         to add a compiler directive.  We do not check for a zero
%         (or near zero) diagonal element since this would interfere
%         with vectorization.  If this makes you nervous put a check
%         in!  It will run much slower.
%
for icol = 1 : n;
dinv(icol) = 1.0e0./a(ja(icol));
end; icol = fix(n+1);
%
%------------- LAST LINE OF SSDS FOLLOWS ----------------------------
end
%DECK SSGS