ScaLAPACK 2.1  2.1
ScaLAPACK: Scalable Linear Algebra PACKage
pdgelqrv.f
Go to the documentation of this file.
1  SUBROUTINE pdgelqrv( M, N, A, IA, JA, DESCA, TAU, WORK )
2 *
3 * -- ScaLAPACK routine (version 1.7) --
4 * University of Tennessee, Knoxville, Oak Ridge National Laboratory,
5 * and University of California, Berkeley.
6 * May 28, 2001
7 *
8 * .. Scalar Arguments ..
9  INTEGER IA, JA, M, N
10 * ..
11 * .. Array Arguments ..
12  INTEGER DESCA( * )
13  DOUBLE PRECISION A( * ), TAU( * ), WORK( * )
14 * ..
15 *
16 * Purpose
17 * =======
18 *
19 * PDGELQRV computes sub( A ) = A(IA:IA+M-1,JA:JA+N-1) from L, Q
20 * computed by PDGELQF.
21 *
22 * Notes
23 * =====
24 *
25 * Each global data object is described by an associated description
26 * vector. This vector stores the information required to establish
27 * the mapping between an object element and its corresponding process
28 * and memory location.
29 *
30 * Let A be a generic term for any 2D block cyclicly distributed array.
31 * Such a global array has an associated description vector DESCA.
32 * In the following comments, the character _ should be read as
33 * "of the global array".
34 *
35 * NOTATION STORED IN EXPLANATION
36 * --------------- -------------- --------------------------------------
37 * DTYPE_A(global) DESCA( DTYPE_ )The descriptor type. In this case,
38 * DTYPE_A = 1.
39 * CTXT_A (global) DESCA( CTXT_ ) The BLACS context handle, indicating
40 * the BLACS process grid A is distribu-
41 * ted over. The context itself is glo-
42 * bal, but the handle (the integer
43 * value) may vary.
44 * M_A (global) DESCA( M_ ) The number of rows in the global
45 * array A.
46 * N_A (global) DESCA( N_ ) The number of columns in the global
47 * array A.
48 * MB_A (global) DESCA( MB_ ) The blocking factor used to distribute
49 * the rows of the array.
50 * NB_A (global) DESCA( NB_ ) The blocking factor used to distribute
51 * the columns of the array.
52 * RSRC_A (global) DESCA( RSRC_ ) The process row over which the first
53 * row of the array A is distributed.
54 * CSRC_A (global) DESCA( CSRC_ ) The process column over which the
55 * first column of the array A is
56 * distributed.
57 * LLD_A (local) DESCA( LLD_ ) The leading dimension of the local
58 * array. LLD_A >= MAX(1,LOCr(M_A)).
59 *
60 * Let K be the number of rows or columns of a distributed matrix,
61 * and assume that its process grid has dimension p x q.
62 * LOCr( K ) denotes the number of elements of K that a process
63 * would receive if K were distributed over the p processes of its
64 * process column.
65 * Similarly, LOCc( K ) denotes the number of elements of K that a
66 * process would receive if K were distributed over the q processes of
67 * its process row.
68 * The values of LOCr() and LOCc() may be determined via a call to the
69 * ScaLAPACK tool function, NUMROC:
70 * LOCr( M ) = NUMROC( M, MB_A, MYROW, RSRC_A, NPROW ),
71 * LOCc( N ) = NUMROC( N, NB_A, MYCOL, CSRC_A, NPCOL ).
72 * An upper bound for these quantities may be computed by:
73 * LOCr( M ) <= ceil( ceil(M/MB_A)/NPROW )*MB_A
74 * LOCc( N ) <= ceil( ceil(N/NB_A)/NPCOL )*NB_A
75 *
76 * Arguments
77 * =========
78 *
79 * M (global input) INTEGER
80 * The number of rows to be operated on, i.e. the number of rows
81 * of the distributed submatrix sub( A ). M >= 0.
82 *
83 * N (global input) INTEGER
84 * The number of columns to be operated on, i.e. the number of
85 * columns of the distributed submatrix sub( A ). N >= 0.
86 *
87 * A (local input/local output) DOUBLE PRECISION pointer into the
88 * local memory to an array of dimension (LLD_A, LOCc(JA+N-1)).
89 * On entry, sub( A ) contains the the factors L and Q computed
90 * by PDGELQF. On exit, the original matrix is restored.
91 *
92 * IA (global input) INTEGER
93 * The row index in the global array A indicating the first
94 * row of sub( A ).
95 *
96 * JA (global input) INTEGER
97 * The column index in the global array A indicating the
98 * first column of sub( A ).
99 *
100 * DESCA (global and local input) INTEGER array of dimension DLEN_.
101 * The array descriptor for the distributed matrix A.
102 *
103 * TAU (local input) DOUBLE PRECISION, array, dimension
104 * LOCr(IA+MIN(M,N)-1). This array contains the scalar factors
105 * TAU of the elementary reflectors computed by PDGELQF. TAU
106 * is tied to the distributed matrix A.
107 *
108 * WORK (local workspace) DOUBLE PRECISION array, dimension
109 * LWORK = MB_A * ( Mp0 + 2*Nq0 + MB_A ), where
110 * Mp0 = NUMROC( M+IROFF, MB_A, MYROW, IAROW, NPROW ) * NB_A,
111 * Nq0 = NUMROC( N+ICOFF, NB_A, MYCOL, IACOL, NPCOL ) * MB_A,
112 * IROFF = MOD( IA-1, MB_A ), ICOFF = MOD( JA-1, NB_A ),
113 * IAROW = INDXG2P( IA, DESCA( MB_ ), MYROW, DESCA( RSRC_ ),
114 * NPROW ),
115 * IACOL = INDXG2P( JA, DESCA( NB_ ), MYCOL, DESCA( CSRC_ ),
116 * NPCOL ),
117 * and NUMROC, INDXG2P are ScaLAPACK tool functions.
118 *
119 * =====================================================================
120 *
121 * .. Parameters ..
122  INTEGER BLOCK_CYCLIC_2D, CSRC_, CTXT_, DLEN_, DTYPE_,
123  $ LLD_, MB_, M_, NB_, N_, RSRC_
124  parameter( block_cyclic_2d = 1, dlen_ = 9, dtype_ = 1,
125  $ ctxt_ = 2, m_ = 3, n_ = 4, mb_ = 5, nb_ = 6,
126  $ rsrc_ = 7, csrc_ = 8, lld_ = 9 )
127  DOUBLE PRECISION ONE, ZERO
128  parameter( one = 1.0d+0, zero = 0.0d+0 )
129 * ..
130 * .. Local Scalars ..
131  CHARACTER COLBTOP, ROWBTOP
132  INTEGER I, IACOL, IAROW, IB, ICOFF, ICTXT, IIA, IL, IN,
133  $ IPT, IPV, IPW, J, JJA, JV, K, MYCOL, MYROW,
134  $ NPCOL, NPROW, NQ
135 * ..
136 * .. Local Arrays ..
137  INTEGER DESCV( DLEN_ )
138 * ..
139 * .. External Subroutines ..
140  EXTERNAL blacs_gridinfo, descset, infog2l, pdlacpy,
141  $ pdlarfb, pdlarft, pdlaset
142 * ..
143 * .. External Functions ..
144  INTEGER ICEIL, NUMROC
145  EXTERNAL iceil, numroc
146 * ..
147 * .. Intrinsic Functions ..
148  INTRINSIC max, min, mod
149 * ..
150 * .. Executable Statements ..
151 *
152 * Get grid parameters
153 *
154  ictxt = desca( ctxt_ )
155  CALL blacs_gridinfo( ictxt, nprow, npcol, myrow, mycol )
156 *
157  k = min( m, n )
158  in = min( iceil( ia, desca( mb_ ) ) * desca( mb_ ), ia+k-1 )
159  il = max( ( (ia+k-2) / desca( mb_ ) ) * desca( mb_ ) + 1, ia )
160 *
161  icoff = mod( ja-1, desca( nb_ ) )
162  CALL infog2l( il, ja, desca, nprow, npcol, myrow, mycol, iia, jja,
163  $ iarow, iacol )
164  nq = numroc( n+icoff, desca( nb_ ), mycol, iacol, npcol )
165  ipv = 1
166  ipt = ipv + nq * desca( mb_ )
167  ipw = ipt + desca( mb_ ) * desca( mb_ )
168  CALL pb_topget( ictxt, 'Broadcast', 'Rowwise', rowbtop )
169  CALL pb_topget( ictxt, 'Broadcast', 'Columnwise', colbtop )
170  CALL pb_topset( ictxt, 'Broadcast', 'Rowwise', ' ' )
171  CALL pb_topset( ictxt, 'Broadcast', 'Columnwise', 'D-ring' )
172 *
173  CALL descset( descv, desca( mb_ ), n + icoff, desca( mb_ ),
174  $ desca( nb_ ), iarow, iacol, ictxt, desca( mb_ ) )
175 *
176  DO 10 i = il, in+1, -desca( mb_ )
177  ib = min( ia+k-i, desca( mb_ ) )
178  j = ja + i - ia
179  jv = 1 + i - ia + icoff
180 *
181 * Compute upper triangular matrix T
182 *
183  CALL pdlarft( 'Forward', 'Rowwise', n-j+ja, ib, a, i, j, desca,
184  $ tau, work( ipt ), work( ipw ) )
185 *
186 * Copy Householder vectors into workspace
187 *
188  CALL pdlacpy( 'Upper', ib, n-j+ja, a, i, j, desca, work( ipv ),
189  $ 1, jv, descv )
190  CALL pdlaset( 'Lower', ib, n-j+ja, zero, one, work( ipv ), 1,
191  $ jv, descv )
192 *
193 * Zeroes the strict upper triangular part of sub( A ) to get
194 * block column of L
195 *
196  CALL pdlaset( 'Upper', ib, n-j+ja-1, zero, zero, a, i, j+1,
197  $ desca )
198 *
199 * Apply block Householder transformation
200 *
201  CALL pdlarfb( 'Right', 'Transpose', 'Forward', 'Rowwise',
202  $ m-i+ia, n-j+ja, ib, work( ipv ), 1, jv, descv,
203  $ work( ipt ), a, i, j, desca, work( ipw ) )
204 *
205  descv( rsrc_ ) = mod( descv( rsrc_ ) + nprow - 1, nprow )
206 *
207  10 CONTINUE
208 *
209 * Handle first block separately
210 *
211  ib = in - ia + 1
212 *
213 * Compute upper triangular matrix T
214 *
215  CALL pdlarft( 'Forward', 'Rowwise', n, ib, a, ia, ja, desca, tau,
216  $ work( ipt ), work( ipw ) )
217 *
218 * Copy Householder vectors into workspace
219 *
220  CALL pdlacpy( 'Upper', ib, n, a, ia, ja, desca, work( ipv ), 1,
221  $ icoff+1, descv )
222  CALL pdlaset( 'Lower', ib, n, zero, one, work, 1, icoff+1, descv )
223 *
224 * Zeroes the strict upper triangular part of sub( A ) to get
225 * block column of L
226 *
227  CALL pdlaset( 'Upper', ib, n-1, zero, zero, a, ia, ja+1, desca )
228 *
229 * Apply block Householder transformation
230 *
231  CALL pdlarfb( 'Right', 'Transpose', 'Forward', 'Rowwise', m, n,
232  $ ib, work( ipv ), 1, icoff+1, descv, work( ipt ), a,
233  $ ia, ja, desca, work( ipw ) )
234 *
235  CALL pb_topset( ictxt, 'Broadcast', 'Rowwise', rowbtop )
236  CALL pb_topset( ictxt, 'Broadcast', 'Columnwise', colbtop )
237 *
238  RETURN
239 *
240 * End of PDGELQRV
241 *
242  END
max
#define max(A, B)
Definition: pcgemr.c:180
infog2l
subroutine infog2l(GRINDX, GCINDX, DESC, NPROW, NPCOL, MYROW, MYCOL, LRINDX, LCINDX, RSRC, CSRC)
Definition: infog2l.f:3
pdlarft
subroutine pdlarft(DIRECT, STOREV, N, K, V, IV, JV, DESCV, TAU, T, WORK)
Definition: pdlarft.f:3
descset
subroutine descset(DESC, M, N, MB, NB, IRSRC, ICSRC, ICTXT, LLD)
Definition: descset.f:3
pdlaset
subroutine pdlaset(UPLO, M, N, ALPHA, BETA, A, IA, JA, DESCA)
Definition: pdblastst.f:6862
pdgelqrv
subroutine pdgelqrv(M, N, A, IA, JA, DESCA, TAU, WORK)
Definition: pdgelqrv.f:2
pdlarfb
subroutine pdlarfb(SIDE, TRANS, DIRECT, STOREV, M, N, K, V, IV, JV, DESCV, T, C, IC, JC, DESCC, WORK)
Definition: pdlarfb.f:3
pdlacpy
subroutine pdlacpy(UPLO, M, N, A, IA, JA, DESCA, B, IB, JB, DESCB)
Definition: pdlacpy.f:3
min
#define min(A, B)
Definition: pcgemr.c:181