ScaLAPACK 2.1  2.1
ScaLAPACK: Scalable Linear Algebra PACKage
pdelget.f
Go to the documentation of this file.
1  SUBROUTINE pdelget( SCOPE, TOP, ALPHA, A, IA, JA, DESCA )
2 *
3 * -- ScaLAPACK tools routine (version 1.7) --
4 * University of Tennessee, Knoxville, Oak Ridge National Laboratory,
5 * and University of California, Berkeley.
6 * May 1, 1997
7 *
8 * .. Scalar Arguments ..
9  CHARACTER*1 SCOPE, TOP
10  INTEGER IA, JA
11  DOUBLE PRECISION ALPHA
12 * ..
13 * .. Array arguments ..
14  INTEGER DESCA( * )
15  DOUBLE PRECISION A( * )
16 * ..
17 *
18 * Purpose
19 * =======
20 *
21 * PDELGET sets alpha to the distributed matrix entry A( IA, JA ).
22 * The value of alpha is set according to the scope.
23 *
24 * Notes
25 * =====
26 *
27 * Each global data object is described by an associated description
28 * vector. This vector stores the information required to establish
29 * the mapping between an object element and its corresponding process
30 * and memory location.
31 *
32 * Let A be a generic term for any 2D block cyclicly distributed array.
33 * Such a global array has an associated description vector DESCA.
34 * In the following comments, the character _ should be read as
35 * "of the global array".
36 *
37 * NOTATION STORED IN EXPLANATION
38 * --------------- -------------- --------------------------------------
39 * DTYPE_A(global) DESCA( DTYPE_ )The descriptor type. In this case,
40 * DTYPE_A = 1.
41 * CTXT_A (global) DESCA( CTXT_ ) The BLACS context handle, indicating
42 * the BLACS process grid A is distribu-
43 * ted over. The context itself is glo-
44 * bal, but the handle (the integer
45 * value) may vary.
46 * M_A (global) DESCA( M_ ) The number of rows in the global
47 * array A.
48 * N_A (global) DESCA( N_ ) The number of columns in the global
49 * array A.
50 * MB_A (global) DESCA( MB_ ) The blocking factor used to distribute
51 * the rows of the array.
52 * NB_A (global) DESCA( NB_ ) The blocking factor used to distribute
53 * the columns of the array.
54 * RSRC_A (global) DESCA( RSRC_ ) The process row over which the first
55 * row of the array A is distributed.
56 * CSRC_A (global) DESCA( CSRC_ ) The process column over which the
57 * first column of the array A is
58 * distributed.
59 * LLD_A (local) DESCA( LLD_ ) The leading dimension of the local
60 * array. LLD_A >= MAX(1,LOCr(M_A)).
61 *
62 * Let K be the number of rows or columns of a distributed matrix,
63 * and assume that its process grid has dimension p x q.
64 * LOCr( K ) denotes the number of elements of K that a process
65 * would receive if K were distributed over the p processes of its
66 * process column.
67 * Similarly, LOCc( K ) denotes the number of elements of K that a
68 * process would receive if K were distributed over the q processes of
69 * its process row.
70 * The values of LOCr() and LOCc() may be determined via a call to the
71 * ScaLAPACK tool function, NUMROC:
72 * LOCr( M ) = NUMROC( M, MB_A, MYROW, RSRC_A, NPROW ),
73 * LOCc( N ) = NUMROC( N, NB_A, MYCOL, CSRC_A, NPCOL ).
74 * An upper bound for these quantities may be computed by:
75 * LOCr( M ) <= ceil( ceil(M/MB_A)/NPROW )*MB_A
76 * LOCc( N ) <= ceil( ceil(N/NB_A)/NPCOL )*NB_A
77 *
78 * Arguments
79 * =========
80 *
81 * SCOPE (global input) CHARACTER*1
82 * The BLACS scope in which alpha is updated.
83 * If SCOPE = 'R', alpha is updated only in the process row
84 * containing A( IA, JA ),
85 * If SCOPE = 'C', alpha is updated only in the process column
86 * containing A( IA, JA ),
87 * If SCOPE = 'A', alpha is updated in all the processes of the
88 * grid,
89 * otherwise alpha is updated only in the process containing
90 * A( IA, JA ).
91 *
92 * TOP (global input) CHARACTER*1
93 * The topology to be used if broadcast is needed.
94 *
95 * ALPHA (global output) DOUBLE PRECISION, the scalar alpha.
96 *
97 * A (local input) DOUBLE PRECISION pointer into the local memory
98 * to an array of dimension (LLD_A,*) containing the local
99 * pieces of the distributed matrix A.
100 *
101 * IA (global input) INTEGER
102 * The row index in the global array A indicating the first
103 * row of sub( A ).
104 *
105 * JA (global input) INTEGER
106 * The column index in the global array A indicating the
107 * first column of sub( A ).
108 *
109 * DESCA (global and local input) INTEGER array of dimension DLEN_.
110 * The array descriptor for the distributed matrix A.
111 *
112 * =====================================================================
113 *
114 * .. Parameters ..
115  INTEGER BLOCK_CYCLIC_2D, CSRC_, CTXT_, DLEN_, DTYPE_,
116  $ LLD_, MB_, M_, NB_, N_, RSRC_
117  parameter( block_cyclic_2d = 1, dlen_ = 9, dtype_ = 1,
118  $ ctxt_ = 2, m_ = 3, n_ = 4, mb_ = 5, nb_ = 6,
119  $ rsrc_ = 7, csrc_ = 8, lld_ = 9 )
120  DOUBLE PRECISION ZERO
121  parameter( zero = 0.0d+0 )
122 * ..
123 * .. Local Scalars ..
124  INTEGER IACOL, IAROW, ICTXT, IIA, IOFFA, JJA, MYCOL,
125  $ MYROW, NPCOL, NPROW
126 * ..
127 * .. External Subroutines ..
128  EXTERNAL blacs_gridinfo, dgebr2d, dgebs2d, infog2l
129 * ..
130 * .. External Functions ..
131  LOGICAL LSAME
132  EXTERNAL lsame
133 * ..
134 * .. Executable Statements ..
135 *
136 * Get grid parameters.
137 *
138  ictxt = desca( ctxt_ )
139  CALL blacs_gridinfo( ictxt, nprow, npcol, myrow, mycol )
140 *
141  CALL infog2l( ia, ja, desca, nprow, npcol, myrow, mycol, iia, jja,
142  $ iarow, iacol )
143 *
144  alpha = zero
145 *
146  IF( lsame( scope, 'R' ) ) THEN
147  IF( myrow.EQ.iarow ) THEN
148  IF( mycol.EQ.iacol ) THEN
149  ioffa = iia+(jja-1)*desca( lld_ )
150  CALL dgebs2d( ictxt, scope, top, 1, 1, a( ioffa ), 1 )
151  alpha = a( ioffa )
152  ELSE
153  CALL dgebr2d( ictxt, scope, top, 1, 1, alpha, 1,
154  $ iarow, iacol )
155  END IF
156  END IF
157  ELSE IF( lsame( scope, 'C' ) ) THEN
158  IF( mycol.EQ.iacol ) THEN
159  IF( myrow.EQ.iarow ) THEN
160  ioffa = iia+(jja-1)*desca( lld_ )
161  CALL dgebs2d( ictxt, scope, top, 1, 1, a( ioffa ), 1 )
162  alpha = a( ioffa )
163  ELSE
164  CALL dgebr2d( ictxt, scope, top, 1, 1, alpha, 1,
165  $ iarow, iacol )
166  END IF
167  END IF
168  ELSE IF( lsame( scope, 'A' ) ) THEN
169  IF( ( myrow.EQ.iarow ).AND.( mycol.EQ.iacol ) ) THEN
170  ioffa = iia+(jja-1)*desca( lld_ )
171  CALL dgebs2d( ictxt, scope, top, 1, 1, a( ioffa ), 1 )
172  alpha = a( ioffa )
173  ELSE
174  CALL dgebr2d( ictxt, scope, top, 1, 1, alpha, 1,
175  $ iarow, iacol )
176  END IF
177  ELSE
178  IF( myrow.EQ.iarow .AND. mycol.EQ.iacol )
179  $ alpha = a( iia+(jja-1)*desca( lld_ ) )
180  END IF
181 *
182  RETURN
183 *
184 * End of PDELGET
185 *
186  END
infog2l
subroutine infog2l(GRINDX, GCINDX, DESC, NPROW, NPCOL, MYROW, MYCOL, LRINDX, LCINDX, RSRC, CSRC)
Definition: infog2l.f:3
pdelget
subroutine pdelget(SCOPE, TOP, ALPHA, A, IA, JA, DESCA)
Definition: pdelget.f:2