[n,nelt,ia,ja,a,isym,nel,iel,jel,el]=ss2lt(n,nelt,ia,ja,a,isym,nel,iel,jel,el);

function [n,nelt,ia,ja,a,isym,nel,iel,jel,el]=ss2lt(n,nelt,ia,ja,a,isym,nel,iel,jel,el);
%***BEGIN PROLOGUE  SS2LT
%***PURPOSE  Lower Triangle Preconditioner SLAP Set Up.
%            Routine to store the lower triangle of a matrix stored
%            in the SLAP Column format.
%***LIBRARY   SLATEC (SLAP)
%***CATEGORY  D2E
%***TYPE      SINGLE PRECISION (SS2LT-S, DS2LT-D)
%***KEYWORDS  LINEAR SYSTEM, LOWER TRIANGLE, 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
%     INTEGER NEL, IEL(NEL), JEL(NEL)
%     REAL    A(NELT), EL(NEL)
%
%     CALL SS2LT( N, NELT, IA, JA, A, ISYM, NEL, IEL, JEL, EL )
%
% *Arguments:
% N      :IN       Integer
%         Order of the Matrix.
% NELT   :IN       Integer.
%         Number of non-zeros stored in A.
% IA     :IN       Integer IA(NELT).
% JA     :IN       Integer JA(NELT).
% A      :IN       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 lower
%         triangle of the matrix is stored.
% NEL    :OUT      Integer.
%         Number of non-zeros in the lower triangle of A.   Also
%         corresponds to the length of the IEL, JEL, EL arrays.
% IEL    :OUT      Integer IEL(NEL).
% JEL    :OUT      Integer JEL(NEL).
% EL     :OUT      Real     EL(NEL).
%         IEL, JEL, EL contain the lower triangle of the A matrix
%         stored in SLAP Column format.  See 'Description', below,
%         for more details bout the SLAP Column format.
%
% *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|
%
%***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  SS2LT
%     .. Scalar Arguments ..
%     .. Array Arguments ..
%     .. Local Scalars ..
persistent i icol j jbgn jend ; 

if isempty(i), i=0; end;
if isempty(icol), icol=0; end;
if isempty(j), j=0; end;
if isempty(jbgn), jbgn=0; end;
if isempty(jend), jend=0; end;
%***FIRST EXECUTABLE STATEMENT  SS2LT
if( isym==0 )
%
%         The matrix is stored non-symmetricly.  Pick out the lower
%         triangle.
%
nel = 0;
for icol = 1 : n;
jel(icol) = fix(nel + 1);
jbgn = fix(ja(icol));
jend = fix(ja(icol+1) - 1);
%VD$ NOVECTOR
for j = jbgn : jend;
if( ia(j)>=icol )
nel = fix(nel + 1);
iel(nel) = fix(ia(j));
el(nel) = a(j);
end;
end; j = fix(jend+1);
end; icol = fix(n+1);
jel(n+1) = fix(nel + 1);
else;
%
%         The matrix is symmetric and only the lower triangle is
%         stored.  Copy it to IEL, JEL, EL.
%
nel = fix(nelt);
for i = 1 : nelt;
iel(i) = fix(ia(i));
el(i) = a(i);
end; i = fix(nelt+1);
for i = 1 : n + 1;
jel(i) = fix(ja(i));
end; i = fix(n + 1+1);
end;
%------------- LAST LINE OF SS2LT FOLLOWS ----------------------------
end
%DECK SS2Y