PDLAPIV(l) | LAPACK auxiliary routine (version 1.5) | PDLAPIV(l) |
NAME¶
PDLAPIV - applie either P (permutation matrix indicated by IPIV) or inv( P ) to a general M-by-N distributed matrix sub( A ) = A(IA:IA+M-1,JA:JA+N-1), resulting in row or column pivotingSYNOPSIS¶
- SUBROUTINE PDLAPIV(
- DIREC, ROWCOL, PIVROC, M, N, A, IA, JA, DESCA, IPIV, IP, JP, DESCIP, IWORK )
PURPOSE¶
PDLAPIV applies either P (permutation matrix indicated by IPIV) or inv( P ) to a general M-by-N distributed matrix sub( A ) = A(IA:IA+M-1,JA:JA+N-1), resulting in row or column pivoting. The pivot vector may be distributed across a process row or a column. The pivot vector should be aligned with the distributed matrix A. This routine will transpose the pivot vector if necessary. For example if the row pivots should be applied to the columns of sub( A ), pass ROWCOL='C' and PIVROC='C'.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)). 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
JP must be 1
IP must be 1
DESCIP(MB_) must equal DESCA(NB_)
DESCIP(NB_) must equal DESCA(MB_)
ARGUMENTS¶
- DIREC (global input) CHARACTER*1
- Specifies in which order the permutation is applied: = 'F' (Forward) Applies pivots Forward from top of matrix. Computes P*sub( A ). = 'B' (Backward) Applies pivots Backward from bottom of matrix. Computes inv( P )*sub( A ).
- ROWCOL (global input) CHARACTER*1
- Specifies if the rows or columns are to be permuted: = 'R' Rows will be permuted, = 'C' Columns will be permuted.
- PIVROC (global input) CHARACTER*1
- Specifies whether IPIV is distributed over a process row or column: = 'R' IPIV distributed over a process row = 'C' IPIV distributed over a process column
- M (global input) INTEGER
- The number of rows to be operated on, i.e. the number of rows of the distributed submatrix sub( A ). M >= 0.
- N (global input) INTEGER
- The number of columns to be operated on, i.e. the number of columns of the distributed submatrix sub( A ). N >= 0.
- A (local input/local output) DOUBLE PRECISION pointer into the
- local memory to an array of dimension (LLD_A, LOCc(JA+N-1)). On entry, this array contains the local pieces of the distributed submatrix sub( A ) to which the row or column interchanges will be applied. On exit, the local pieces of the permuted distributed submatrix.
- 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.
- IPIV (local input) INTEGER array, dimension >= LOCr(M_A)+MB_A
- if ROWCOL='R', otherwise LOCc(N_A)+NB_A. It contains the pivoting information. IPIV(i) is the global row (column), local row (column) i was swapped with. The last piece of the array of size MB_A (resp. NB_A) is used as workspace. This array is tied to the distributed matrix A.
- IWORK (local workspace) INTEGER array, dimension (LDW)
- where LDW is equal to the workspace necessary for transposition, and the storage of the tranposed IPIV: Let LCM be the least common multiple of NPROW and NPCOL. IF( ROWCOL.EQ.'R' .AND. PIVROC.EQ.'R' ) THEN IF( NPROW.EQ.NPCOL ) THEN LDW = LOCr( N_P + MOD(JP-1, NB_P) ) + NB_P ELSE LDW = LOCr( N_P + MOD(JP-1, NB_P) ) + NB_P * CEIL( CEIL(LOCc(N_P)/NB_P) / (LCM/NPCOL) ) END IF ELSE IF( ROWCOL.EQ.'C' .AND. PIVROC.EQ.'C' ) THEN IF( NPROW.EQ.NPCOL ) THEN LDW = LOCc( M_P + MOD(IP-1, MB_P) ) + MB_P ELSE LDW = LOCc( M_P + MOD(IP-1, MB_P) ) + MB_P * CEIL( CEIL(LOCr(M_P)/MB_P) / (LCM/NPROW) ) END IF ELSE IWORK is not referenced. END IF
12 May 1997 | LAPACK version 1.5 |