PSLASMSUB(l) | LAPACK routine (version 1.5 ) | PSLASMSUB(l) |
NAME¶
PSLASMSUB - look for a small subdiagonal element from the bottom of the matrix that it can safely set to zeroSYNOPSIS¶
- SUBROUTINE PSLASMSUB(
- A, DESCA, I, L, K, SMLNUM, BUF, LWORK )
- INTEGER
- I, K, L, LWORK
- REAL
- SMLNUM
- INTEGER
- DESCA( * )
- REAL
- A( * ), BUF( * )
PURPOSE¶
PSLASMSUB looks for a small subdiagonal element from the bottomof the matrix that it can safely set to zero.
DTYPE_A = 1.
the BLACS process grid A is distribu-
ted over. The context itself is glo-
bal, but the handle (the integer
value) may vary.
array A.
array A.
the rows of the array.
the columns of the array.
row of the array A is distributed. CSRC_A (global) DESCA( CSRC_ ) The process column over which the
first column of the array A is
distributed.
array. LLD_A >= MAX(1,LOCr(M_A)).
LOCr( M ) = NUMROC( M, MB_A, MYROW, RSRC_A, NPROW ),
LOCc( N ) = NUMROC( N, NB_A, MYCOL, CSRC_A, NPCOL ). An upper bound for these quantities may be computed by:
LOCr( M ) <= ceil( ceil(M/MB_A)/NPROW )*MB_A
LOCc( N ) <= ceil( ceil(N/NB_A)/NPCOL )*NB_A
ARGUMENTS¶
- A (global input) REAL array, dimension
- (DESCA(LLD_),*) On entry, the Hessenberg matrix whose tridiagonal part is being scanned. Unchanged on exit.
- DESCA (global and local input) INTEGER array of dimension DLEN_.
- The array descriptor for the distributed matrix A.
- I (global input) INTEGER
- The global location of the bottom of the unreduced submatrix of A. Unchanged on exit.
- L (global input) INTEGER
- The global location of the top of the unreduced submatrix of A. Unchanged on exit.
- K (global output) INTEGER
- On exit, this yields the bottom portion of the unreduced submatrix. This will satisfy: L <= M <= I-1.
- SMLNUM (global input) REAL
- On entry, a "small number" for the given matrix. Unchanged on exit.
- BUF (local output) REAL array of size LWORK.
- LWORK (global input) INTEGER
- On exit, LWORK is the size of the work buffer. This must be
at least 2*Ceil( Ceil( (I-L)/HBL ) / LCM(NPROW,NPCOL) ) Here LCM is least
common multiple, and NPROWxNPCOL is the logical grid size.
12 May 1997 | LAPACK version 1.5 |