# SRC/cgsitrf.c File Reference

`#include "slu_cdefs.h"`

## Functions
void | cgsitrf (superlu_options_t *options, SuperMatrix *A, int relax, int panel_size, int *etree, void *work, int lwork, int *perm_c, int *perm_r, SuperMatrix *L, SuperMatrix *U, SuperLUStat_t *stat, int *info)

## Function Documentation

void cgsitrf | ( | superlu_options_t * | options,
|  | SuperMatrix * | A,
|  | int | relax,
|  | int | panel_size,
|  | int * | etree,
|  | void * | work,
|  | int | lwork,
|  | int * | perm_c,
|  | int * | perm_r,
|  | SuperMatrix * | L,
|  | SuperMatrix * | U,
|  | SuperLUStat_t * | stat,
|  | int * | info |
| ) |  |  |

     Purpose
     =======

     CGSITRF computes an ILU factorization of a general sparse m-by-n
     matrix A using partial pivoting with row interchanges.
     The factorization has the form
         Pr * A = L * U
     where Pr is a row permutation matrix, L is lower triangular with unit
     diagonal elements (lower trapezoidal if A->nrow > A->ncol), and U is upper
     triangular (upper trapezoidal if A->nrow < A->ncol).

     See supermatrix.h for the definition of 'SuperMatrix' structure.

     Arguments
     =========

     options (input) superlu_options_t*
    	   The structure defines the input parameters to control
    	   how the ILU decomposition will be performed.

     A	    (input) SuperMatrix*
    	    Original matrix A, permuted by columns, of dimension
    	    (A->nrow, A->ncol). The type of A can be:
    	    Stype = SLU_NCP; Dtype = SLU_C; Mtype = SLU_GE.

     relax    (input) int
    	    To control degree of relaxing supernodes. If the number
    	    of nodes (columns) in a subtree of the elimination tree is less
    	    than relax, this subtree is considered as one supernode,
    	    regardless of the row structures of those columns.

     panel_size (input) int
    	    A panel consists of at most panel_size consecutive columns.

     etree    (input) int*, dimension (A->ncol)
    	    Elimination tree of A'*A.
    	    Note: etree is a vector of parent pointers for a forest whose
    	    vertices are the integers 0 to A->ncol-1; etree[root]==A->ncol.
    	    On input, the columns of A should be permuted so that the
    	    etree is in a certain postorder.

     work     (input/output) void*, size (lwork) (in bytes)
    	    User-supplied work space and space for the output data structures.
    	    Not referenced if lwork = 0;

     lwork   (input) int
    	   Specifies the size of work array in bytes.
    	   = 0:  allocate space internally by system malloc;
    	   > 0:  use user-supplied work array of length lwork in bytes,
    		 returns error if space runs out.
    	   = -1: the routine guesses the amount of space needed without
    		 performing the factorization, and returns it in
    		 *info; no other side effects.

     perm_c   (input) int*, dimension (A->ncol)
    	    Column permutation vector, which defines the
    	    permutation matrix Pc; perm_c[i] = j means column i of A is
    	    in position j in A*Pc.
    	    When searching for diagonal, perm_c[*] is applied to the
    	    row subscripts of A, so that diagonal threshold pivoting
    	    can find the diagonal of A, rather than that of A*Pc.

     perm_r   (input/output) int*, dimension (A->nrow)
    	    Row permutation vector which defines the permutation matrix Pr,
    	    perm_r[i] = j means row i of A is in position j in Pr*A.
    	    If options->Fact = SamePattern_SameRowPerm, the pivoting routine
    	       will try to use the input perm_r, unless a certain threshold
    	       criterion is violated. In that case, perm_r is overwritten by
    	       a new permutation determined by partial pivoting or diagonal
    	       threshold pivoting.
    	    Otherwise, perm_r is output argument;

     L	    (output) SuperMatrix*
    	    The factor L from the factorization Pr*A=L*U; use compressed row
    	    subscripts storage for supernodes, i.e., L has type:
    	    Stype = SLU_SC, Dtype = SLU_C, Mtype = SLU_TRLU.

     U	    (output) SuperMatrix*
    	    The factor U from the factorization Pr*A*Pc=L*U. Use column-wise
    	    storage scheme, i.e., U has types: Stype = SLU_NC,
    	    Dtype = SLU_C, Mtype = SLU_TRU.

     stat     (output) SuperLUStat_t*
    	    Record the statistics on runtime and floating-point operation count.
    	    See slu_util.h for the definition of 'SuperLUStat_t'.

     info     (output) int*
    	    = 0: successful exit
    	    < 0: if info = -i, the i-th argument had an illegal value
    	    > 0: if info = i, and i is
    	       <= A->ncol: number of zero pivots. They are replaced by small
    		  entries according to options->ILU_FillTol.
    	       > A->ncol: number of bytes allocated when memory allocation
    		  failure occurred, plus A->ncol. If lwork = -1, it is
    		  the estimated amount of space needed, plus A->ncol.

     ======================================================================

     Local Working Arrays:
     ======================
       m = number of rows in the matrix
       n = number of columns in the matrix

       marker[0:3*m-1]: marker[i] = j means that node i has been
    	reached when working on column j.
    	Storage: relative to original row subscripts
    	NOTE: There are 4 of them:
    	      marker/marker1 are used for panel dfs, see (ilu_)dpanel_dfs.c;
    	      marker2 is used for inner-factorization, see (ilu)_dcolumn_dfs.c;
    	      marker_relax(has its own space) is used for relaxed supernodes.

       parent[0:m-1]: parent vector used during dfs
    	Storage: relative to new row subscripts

       xplore[0:m-1]: xplore[i] gives the location of the next (dfs)
    	unexplored neighbor of i in lsub[*]

       segrep[0:nseg-1]: contains the list of supernodal representatives
    	in topological order of the dfs. A supernode representative is the
    	last column of a supernode.
    	The maximum size of segrep[] is n.

       repfnz[0:W*m-1]: for a nonzero segment U[*,j] that ends at a
    	supernodal representative r, repfnz[r] is the location of the first
    	nonzero in this segment.  It is also used during the dfs: repfnz[r]>0
    	indicates the supernode r has been explored.
    	NOTE: There are W of them, each used for one column of a panel.

       panel_lsub[0:W*m-1]: temporary for the nonzeros row indices below
    	the panel diagonal. These are filled in during dpanel_dfs(), and are
    	used later in the inner LU factorization within the panel.
    	panel_lsub[]/dense[] pair forms the SPA data structure.
    	NOTE: There are W of them.

       dense[0:W*m-1]: sparse accumulating (SPA) vector for intermediate values;
    		   NOTE: there are W of them.

       tempv[0:*]: real temporary used for dense numeric kernels;
    	The size of this array is defined by NUM_TEMPV() in slu_util.h.
    	It is also used by the dropping routine ilu_ddrop_row().