/*! @file ilu_dpivotL.c
* \brief Performs numerical pivoting
*
*
* -- SuperLU routine (version 4.0) --
* Lawrence Berkeley National Laboratory
* June 30, 2009
*
*/
#include
#include
#include "slu_ddefs.h"
#ifndef SGN
#define SGN(x) ((x)>=0?1:-1)
#endif
/*! \brief
*
*
* Purpose
* =======
* Performs the numerical pivoting on the current column of L,
* and the CDIV operation.
*
* Pivot policy:
* (1) Compute thresh = u * max_(i>=j) abs(A_ij);
* (2) IF user specifies pivot row k and abs(A_kj) >= thresh THEN
* pivot row = k;
* ELSE IF abs(A_jj) >= thresh THEN
* pivot row = j;
* ELSE
* pivot row = m;
*
* Note: If you absolutely want to use a given pivot order, then set u=0.0.
*
* Return value: 0 success;
* i > 0 U(i,i) is exactly zero.
*
*/
int
ilu_dpivotL(
const int jcol, /* in */
const double u, /* in - diagonal pivoting threshold */
int *usepr, /* re-use the pivot sequence given by
* perm_r/iperm_r */
int *perm_r, /* may be modified */
int diagind, /* diagonal of Pc*A*Pc' */
int *swap, /* in/out record the row permutation */
int *iswap, /* in/out inverse of swap, it is the same as
perm_r after the factorization */
int *marker, /* in */
int *pivrow, /* in/out, as an input if *usepr!=0 */
double fill_tol, /* in - fill tolerance of current column
* used for a singular column */
milu_t milu, /* in */
double drop_sum, /* in - computed in ilu_dcopy_to_ucol()
(MILU only) */
GlobalLU_t *Glu, /* modified - global LU data structures */
SuperLUStat_t *stat /* output */
)
{
int n; /* number of columns */
int fsupc; /* first column in the supernode */
int nsupc; /* no of columns in the supernode */
int nsupr; /* no of rows in the supernode */
int lptr; /* points to the starting subscript of the supernode */
register int pivptr;
int old_pivptr, diag, ptr0;
register double pivmax, rtemp;
double thresh;
double temp;
double *lu_sup_ptr;
double *lu_col_ptr;
int *lsub_ptr;
register int isub, icol, k, itemp;
int *lsub, *xlsub;
double *lusup;
int *xlusup;
flops_t *ops = stat->ops;
int info;
/* Initialize pointers */
n = Glu->n;
lsub = Glu->lsub;
xlsub = Glu->xlsub;
lusup = Glu->lusup;
xlusup = Glu->xlusup;
fsupc = (Glu->xsup)[(Glu->supno)[jcol]];
nsupc = jcol - fsupc; /* excluding jcol; nsupc >= 0 */
lptr = xlsub[fsupc];
nsupr = xlsub[fsupc+1] - lptr;
lu_sup_ptr = &lusup[xlusup[fsupc]]; /* start of the current supernode */
lu_col_ptr = &lusup[xlusup[jcol]]; /* start of jcol in the supernode */
lsub_ptr = &lsub[lptr]; /* start of row indices of the supernode */
/* Determine the largest abs numerical value for partial pivoting;
Also search for user-specified pivot, and diagonal element. */
pivmax = -1.0;
pivptr = nsupc;
diag = EMPTY;
old_pivptr = nsupc;
ptr0 = EMPTY;
for (isub = nsupc; isub < nsupr; ++isub) {
if (marker[lsub_ptr[isub]] > jcol)
continue; /* do not overlap with a later relaxed supernode */
switch (milu) {
case SMILU_1:
rtemp = fabs(lu_col_ptr[isub] + drop_sum);
break;
case SMILU_2:
case SMILU_3:
/* In this case, drop_sum contains the sum of the abs. value */
rtemp = fabs(lu_col_ptr[isub]);
break;
case SILU:
default:
rtemp = fabs(lu_col_ptr[isub]);
break;
}
if (rtemp > pivmax) { pivmax = rtemp; pivptr = isub; }
if (*usepr && lsub_ptr[isub] == *pivrow) old_pivptr = isub;
if (lsub_ptr[isub] == diagind) diag = isub;
if (ptr0 == EMPTY) ptr0 = isub;
}
if (milu == SMILU_2 || milu == SMILU_3) pivmax += drop_sum;
/* Test for singularity */
if (pivmax < 0.0) {
fprintf(stderr, "[0]: jcol=%d, SINGULAR!!!\n", jcol);
fflush(stderr);
exit(1);
}
if ( pivmax == 0.0 ) {
if (diag != EMPTY)
*pivrow = lsub_ptr[pivptr = diag];
else if (ptr0 != EMPTY)
*pivrow = lsub_ptr[pivptr = ptr0];
else {
/* look for the first row which does not
belong to any later supernodes */
for (icol = jcol; icol < n; icol++)
if (marker[swap[icol]] <= jcol) break;
if (icol >= n) {
fprintf(stderr, "[1]: jcol=%d, SINGULAR!!!\n", jcol);
fflush(stderr);
exit(1);
}
*pivrow = swap[icol];
/* pick up the pivot row */
for (isub = nsupc; isub < nsupr; ++isub)
if ( lsub_ptr[isub] == *pivrow ) { pivptr = isub; break; }
}
pivmax = fill_tol;
lu_col_ptr[pivptr] = pivmax;
*usepr = 0;
#ifdef DEBUG
printf("[0] ZERO PIVOT: FILL (%d, %d).\n", *pivrow, jcol);
fflush(stdout);
#endif
info =jcol + 1;
} /* if (*pivrow == 0.0) */
else {
thresh = u * pivmax;
/* Choose appropriate pivotal element by our policy. */
if ( *usepr ) {
switch (milu) {
case SMILU_1:
rtemp = fabs(lu_col_ptr[old_pivptr] + drop_sum);
break;
case SMILU_2:
case SMILU_3:
rtemp = fabs(lu_col_ptr[old_pivptr]) + drop_sum;
break;
case SILU:
default:
rtemp = fabs(lu_col_ptr[old_pivptr]);
break;
}
if ( rtemp != 0.0 && rtemp >= thresh ) pivptr = old_pivptr;
else *usepr = 0;
}
if ( *usepr == 0 ) {
/* Use diagonal pivot? */
if ( diag >= 0 ) { /* diagonal exists */
switch (milu) {
case SMILU_1:
rtemp = fabs(lu_col_ptr[diag] + drop_sum);
break;
case SMILU_2:
case SMILU_3:
rtemp = fabs(lu_col_ptr[diag]) + drop_sum;
break;
case SILU:
default:
rtemp = fabs(lu_col_ptr[diag]);
break;
}
if ( rtemp != 0.0 && rtemp >= thresh ) pivptr = diag;
}
*pivrow = lsub_ptr[pivptr];
}
info = 0;
/* Reset the diagonal */
switch (milu) {
case SMILU_1:
lu_col_ptr[pivptr] += drop_sum;
break;
case SMILU_2:
case SMILU_3:
lu_col_ptr[pivptr] += SGN(lu_col_ptr[pivptr]) * drop_sum;
break;
case SILU:
default:
break;
}
} /* else */
/* Record pivot row */
perm_r[*pivrow] = jcol;
if (jcol < n - 1) {
register int t1, t2, t;
t1 = iswap[*pivrow]; t2 = jcol;
if (t1 != t2) {
t = swap[t1]; swap[t1] = swap[t2]; swap[t2] = t;
t1 = swap[t1]; t2 = t;
t = iswap[t1]; iswap[t1] = iswap[t2]; iswap[t2] = t;
}
} /* if (jcol < n - 1) */
/* Interchange row subscripts */
if ( pivptr != nsupc ) {
itemp = lsub_ptr[pivptr];
lsub_ptr[pivptr] = lsub_ptr[nsupc];
lsub_ptr[nsupc] = itemp;
/* Interchange numerical values as well, for the whole snode, such
* that L is indexed the same way as A.
*/
for (icol = 0; icol <= nsupc; icol++) {
itemp = pivptr + icol * nsupr;
temp = lu_sup_ptr[itemp];
lu_sup_ptr[itemp] = lu_sup_ptr[nsupc + icol*nsupr];
lu_sup_ptr[nsupc + icol*nsupr] = temp;
}
} /* if */
/* cdiv operation */
ops[FACT] += nsupr - nsupc;
temp = 1.0 / lu_col_ptr[nsupc];
for (k = nsupc+1; k < nsupr; k++) lu_col_ptr[k] *= temp;
return info;
}