ScaLAPACK 2.1  2.1
ScaLAPACK: Scalable Linear Algebra PACKage
pdelset2.f
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1  SUBROUTINE pdelset2( ALPHA, A, IA, JA, DESCA, BETA )
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  INTEGER IA, JA
10  DOUBLE PRECISION ALPHA, BETA
11 * ..
12 * .. Array arguments ..
13  INTEGER DESCA( * )
14  DOUBLE PRECISION A( * )
15 * ..
16 *
17 * Purpose
18 * =======
19 *
20 * PDELSET2 sets alpha to the distributed matrix entry A(IA,JA)
21 * and A(IA,JA) to beta.
22 *
23 * Notes
24 * =====
25 *
26 * Each global data object is described by an associated description
27 * vector. This vector stores the information required to establish
28 * the mapping between an object element and its corresponding process
29 * and memory location.
30 *
31 * Let A be a generic term for any 2D block cyclicly distributed array.
32 * Such a global array has an associated description vector DESCA.
33 * In the following comments, the character _ should be read as
34 * "of the global array".
35 *
36 * NOTATION STORED IN EXPLANATION
37 * --------------- -------------- --------------------------------------
38 * DTYPE_A(global) DESCA( DTYPE_ )The descriptor type. In this case,
39 * DTYPE_A = 1.
40 * CTXT_A (global) DESCA( CTXT_ ) The BLACS context handle, indicating
41 * the BLACS process grid A is distribu-
42 * ted over. The context itself is glo-
43 * bal, but the handle (the integer
44 * value) may vary.
45 * M_A (global) DESCA( M_ ) The number of rows in the global
46 * array A.
47 * N_A (global) DESCA( N_ ) The number of columns in the global
48 * array A.
49 * MB_A (global) DESCA( MB_ ) The blocking factor used to distribute
50 * the rows of the array.
51 * NB_A (global) DESCA( NB_ ) The blocking factor used to distribute
52 * the columns of the array.
53 * RSRC_A (global) DESCA( RSRC_ ) The process row over which the first
54 * row of the array A is distributed.
55 * CSRC_A (global) DESCA( CSRC_ ) The process column over which the
56 * first column of the array A is
57 * distributed.
58 * LLD_A (local) DESCA( LLD_ ) The leading dimension of the local
59 * array. LLD_A >= MAX(1,LOCr(M_A)).
60 *
61 * Let K be the number of rows or columns of a distributed matrix,
62 * and assume that its process grid has dimension p x q.
63 * LOCr( K ) denotes the number of elements of K that a process
64 * would receive if K were distributed over the p processes of its
65 * process column.
66 * Similarly, LOCc( K ) denotes the number of elements of K that a
67 * process would receive if K were distributed over the q processes of
68 * its process row.
69 * The values of LOCr() and LOCc() may be determined via a call to the
70 * ScaLAPACK tool function, NUMROC:
71 * LOCr( M ) = NUMROC( M, MB_A, MYROW, RSRC_A, NPROW ),
72 * LOCc( N ) = NUMROC( N, NB_A, MYCOL, CSRC_A, NPCOL ).
73 * An upper bound for these quantities may be computed by:
74 * LOCr( M ) <= ceil( ceil(M/MB_A)/NPROW )*MB_A
75 * LOCc( N ) <= ceil( ceil(N/NB_A)/NPCOL )*NB_A
76 *
77 * Arguments
78 * =========
79 *
80 * ALPHA (local output) DOUBLE PRECISION
81 * The scalar alpha.
82 *
83 * A (local input/local ouput) DOUBLE PRECISION pointer into the
84 * local memory to an array of dimension (LLD_A,*) containing
85 * the local pieces of the distributed matrix A.
86 *
87 * IA (global input) INTEGER
88 * The row index in the global array A indicating the first
89 * row of sub( A ).
90 *
91 * JA (global input) INTEGER
92 * The column index in the global array A indicating the
93 * first column of sub( A ).
94 *
95 * DESCA (global and local input) INTEGER array of dimension DLEN_.
96 * The array descriptor for the distributed matrix A.
97 *
98 * BETA (local input) DOUBLE PRECISION
99 * The scalar beta.
100 *
101 * =====================================================================
102 *
103 * .. Parameters ..
104  INTEGER BLOCK_CYCLIC_2D, CSRC_, CTXT_, DLEN_, DTYPE_,
105  $ LLD_, MB_, M_, NB_, N_, RSRC_
106  parameter( block_cyclic_2d = 1, dlen_ = 9, dtype_ = 1,
107  $ ctxt_ = 2, m_ = 3, n_ = 4, mb_ = 5, nb_ = 6,
108  $ rsrc_ = 7, csrc_ = 8, lld_ = 9 )
109  DOUBLE PRECISION ZERO
110  parameter( zero = 0.0d+0 )
111 * ..
112 * .. Local Scalars ..
113  INTEGER IACOL, IAROW, IIA, IOFFA, JJA, MYCOL, MYROW,
114  $ NPCOL, NPROW
115 * ..
116 * .. External Subroutines ..
117  EXTERNAL blacs_gridinfo, infog2l
118 * ..
119 * .. Executable Statements ..
120 *
121 * Get grid parameters.
122 *
123  CALL blacs_gridinfo( desca( ctxt_ ), nprow, npcol, myrow, mycol )
124 *
125  CALL infog2l( ia, ja, desca, nprow, npcol, myrow, mycol, iia, jja,
126  $ iarow, iacol )
127 *
128  IF( myrow.EQ.iarow .AND. mycol.EQ.iacol ) THEN
129  ioffa = iia+(jja-1)*desca( lld_ )
130  alpha = a( ioffa )
131  a( ioffa ) = beta
132  ELSE
133  alpha = zero
134  END IF
135 *
136  RETURN
137 *
138 * End of PDELSET2
139 *
140  END
infog2l
subroutine infog2l(GRINDX, GCINDX, DESC, NPROW, NPCOL, MYROW, MYCOL, LRINDX, LCINDX, RSRC, CSRC)
Definition: infog2l.f:3
pdelset2
subroutine pdelset2(ALPHA, A, IA, JA, DESCA, BETA)
Definition: pdelset2.f:2