table of contents
PSLAQSY(l) | LAPACK auxiliary routine (version 1.5) | PSLAQSY(l) |
NAME¶
PSLAQSY - equilibrate a symmetric distributed matrix sub( A ) = A(IA:IA+N-1,JA:JA+N-1) using the scaling factors in the vectors SR and SCSYNOPSIS¶
- SUBROUTINE PSLAQSY(
- UPLO, N, A, IA, JA, DESCA, SR, SC, SCOND, AMAX, EQUED )
PURPOSE¶
PSLAQSY equilibrates a symmetric distributed matrix sub( A ) = A(IA:IA+N-1,JA:JA+N-1) using the scaling factors in the vectors SR and SC. NotesDTYPE_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)). Let K be the number of rows or columns of a distributed matrix, and assume that its process grid has dimension p x q.
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¶
- UPLO (global input) CHARACTER
- Specifies whether the upper or lower triangular part of the symmetric
distributed matrix sub( A ) is to be referenced:
- N (global input) INTEGER
- The number of rows and columns to be operated on, i.e. the order of the distributed submatrix sub( A ). N >= 0.
- A (input/output) REAL pointer into the local
- memory to an array of local dimension (LLD_A,LOCc(JA+N-1)). On entry, the
local pieces of the distributed symmetric matrix sub( A ). If UPLO = 'U',
the leading N-by-N upper triangular part of sub( A ) contains the upper
triangular part of the matrix, and the strictly lower triangular part of
sub( A ) is not referenced. If UPLO = 'L', the leading N-by-N lower
triangular part of sub( A ) contains the lower triangular part of the
matrix, and the strictly upper trian- gular part of sub( A ) is not
referenced. On exit, if EQUED = 'Y', the equilibrated matrix:
- IA (global input) INTEGER
- The row index in the global array A indicating the first row of sub( A ).
- JA (global input) INTEGER
- The column index in the global array A indicating the first column of sub( A ).
- DESCA (global and local input) INTEGER array of dimension DLEN_.
- The array descriptor for the distributed matrix A.
- SR (local input) REAL array, dimension LOCr(M_A)
- The scale factors for A(IA:IA+M-1,JA:JA+N-1). SR is aligned with the distributed matrix A, and replicated across every process column. SR is tied to the distributed matrix A.
- SC (local input) REAL array, dimension LOCc(N_A)
- The scale factors for sub( A ). SC is aligned with the dis- tributed matrix A, and replicated down every process row. SC is tied to the distributed matrix A.
- SCOND (global input) REAL
- Ratio of the smallest SR(i) (respectively SC(j)) to the largest SR(i) (respectively SC(j)), with IA <= i <= IA+N-1 and JA <= j <= JA+N-1.
- AMAX (global input) REAL
- Absolute value of the largest distributed submatrix entry.
- EQUED (output) CHARACTER*1
- Specifies whether or not equilibration was done. = 'N': No equilibration.
PARAMETERS¶
THRESH is a threshold value used to decide if scaling should be done based on the ratio of the scaling factors. If SCOND < THRESH, scaling is done. LARGE and SMALL are threshold values used to decide if scaling should be done based on the absolute size of the largest matrix element. If AMAX > LARGE or AMAX < SMALL, scaling is done.12 May 1997 | LAPACK version 1.5 |