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ScaLAPACK
2.0.2
ScaLAPACK: Scalable Linear Algebra PACKage
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ScaLAPACK
2.0.2
ScaLAPACK: Scalable Linear Algebra PACKage
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00001 SUBROUTINE DESCINIT( DESC, M, N, MB, NB, IRSRC, ICSRC, ICTXT, 00002 $ LLD, INFO ) 00003 * 00004 * -- ScaLAPACK tools routine (version 1.7) -- 00005 * University of Tennessee, Knoxville, Oak Ridge National Laboratory, 00006 * and University of California, Berkeley. 00007 * May 1, 1997 00008 * 00009 * .. Scalar Arguments .. 00010 INTEGER ICSRC, ICTXT, INFO, IRSRC, LLD, M, MB, N, NB 00011 * .. 00012 * .. Array Arguments .. 00013 INTEGER DESC( * ) 00014 * .. 00015 * 00016 * Purpose 00017 * ======= 00018 * 00019 * DESCINIT initializes the descriptor vector with the 8 input arguments 00020 * M, N, MB, NB, IRSRC, ICSRC, ICTXT, LLD. 00021 * 00022 * Notes 00023 * ===== 00024 * 00025 * Each global data object is described by an associated description 00026 * vector. This vector stores the information required to establish 00027 * the mapping between an object element and its corresponding process 00028 * and memory location. 00029 * 00030 * Let A be a generic term for any 2D block cyclicly distributed array. 00031 * Such a global array has an associated description vector DESCA. 00032 * In the following comments, the character _ should be read as 00033 * "of the global array". 00034 * 00035 * NOTATION STORED IN EXPLANATION 00036 * --------------- -------------- -------------------------------------- 00037 * DTYPE_A(global) DESCA( DTYPE_ )The descriptor type. In this case, 00038 * DTYPE_A = 1. 00039 * CTXT_A (global) DESCA( CTXT_ ) The BLACS context handle, indicating 00040 * the BLACS process grid A is distribu- 00041 * ted over. The context itself is glo- 00042 * bal, but the handle (the integer 00043 * value) may vary. 00044 * M_A (global) DESCA( M_ ) The number of rows in the global 00045 * array A. 00046 * N_A (global) DESCA( N_ ) The number of columns in the global 00047 * array A. 00048 * MB_A (global) DESCA( MB_ ) The blocking factor used to distribute 00049 * the rows of the array. 00050 * NB_A (global) DESCA( NB_ ) The blocking factor used to distribute 00051 * the columns of the array. 00052 * RSRC_A (global) DESCA( RSRC_ ) The process row over which the first 00053 * row of the array A is distributed. 00054 * CSRC_A (global) DESCA( CSRC_ ) The process column over which the 00055 * first column of the array A is 00056 * distributed. 00057 * LLD_A (local) DESCA( LLD_ ) The leading dimension of the local 00058 * array. LLD_A >= MAX(1,LOCr(M_A)). 00059 * 00060 * Let K be the number of rows or columns of a distributed matrix, 00061 * and assume that its process grid has dimension p x q. 00062 * LOCr( K ) denotes the number of elements of K that a process 00063 * would receive if K were distributed over the p processes of its 00064 * process column. 00065 * Similarly, LOCc( K ) denotes the number of elements of K that a 00066 * process would receive if K were distributed over the q processes of 00067 * its process row. 00068 * The values of LOCr() and LOCc() may be determined via a call to the 00069 * ScaLAPACK tool function, NUMROC: 00070 * LOCr( M ) = NUMROC( M, MB_A, MYROW, RSRC_A, NPROW ), 00071 * LOCc( N ) = NUMROC( N, NB_A, MYCOL, CSRC_A, NPCOL ). 00072 * An upper bound for these quantities may be computed by: 00073 * LOCr( M ) <= ceil( ceil(M/MB_A)/NPROW )*MB_A 00074 * LOCc( N ) <= ceil( ceil(N/NB_A)/NPCOL )*NB_A 00075 * 00076 * Arguments 00077 * ========= 00078 * 00079 * DESC (output) INTEGER array of dimension DLEN_. 00080 * The array descriptor of a distributed matrix to be set. 00081 * 00082 * M (global input) INTEGER 00083 * The number of rows in the distributed matrix. M >= 0. 00084 * 00085 * N (global input) INTEGER 00086 * The number of columns in the distributed matrix. N >= 0. 00087 * 00088 * MB (global input) INTEGER 00089 * The blocking factor used to distribute the rows of the 00090 * matrix. MB >= 1. 00091 * 00092 * NB (global input) INTEGER 00093 * The blocking factor used to distribute the columns of the 00094 * matrix. NB >= 1. 00095 * 00096 * IRSRC (global input) INTEGER 00097 * The process row over which the first row of the matrix is 00098 * distributed. 0 <= IRSRC < NPROW. 00099 * 00100 * ICSRC (global input) INTEGER 00101 * The process column over which the first column of the 00102 * matrix is distributed. 0 <= ICSRC < NPCOL. 00103 * 00104 * ICTXT (global input) INTEGER 00105 * The BLACS context handle, indicating the global context of 00106 * the operation on the matrix. The context itself is global. 00107 * 00108 * LLD (local input) INTEGER 00109 * The leading dimension of the local array storing the local 00110 * blocks of the distributed matrix. LLD >= MAX(1,LOCr(M)). 00111 * 00112 * INFO (output) INTEGER 00113 * = 0: successful exit 00114 * < 0: if INFO = -i, the i-th argument had an illegal value 00115 * 00116 * Note 00117 * ==== 00118 * 00119 * If the routine can recover from an erroneous input argument, it will 00120 * return an acceptable descriptor vector. For example, if LLD = 0 on 00121 * input, DESC(LLD_) will contain the smallest leading dimension 00122 * required to store the specified M-by-N distributed matrix, INFO 00123 * will be set -9 in that case. 00124 * 00125 * ===================================================================== 00126 * 00127 * .. Parameters .. 00128 INTEGER BLOCK_CYCLIC_2D, CSRC_, CTXT_, DLEN_, DTYPE_, 00129 $ LLD_, MB_, M_, NB_, N_, RSRC_ 00130 PARAMETER ( BLOCK_CYCLIC_2D = 1, DLEN_ = 9, DTYPE_ = 1, 00131 $ CTXT_ = 2, M_ = 3, N_ = 4, MB_ = 5, NB_ = 6, 00132 $ RSRC_ = 7, CSRC_ = 8, LLD_ = 9 ) 00133 * .. 00134 * .. Local Scalars .. 00135 INTEGER MYCOL, MYROW, NPCOL, NPROW 00136 * .. 00137 * .. External Subroutines .. 00138 EXTERNAL BLACS_GRIDINFO, PXERBLA 00139 * .. 00140 * .. External Functions .. 00141 INTEGER NUMROC 00142 EXTERNAL NUMROC 00143 * .. 00144 * .. Intrinsic Functions .. 00145 INTRINSIC MAX, MIN 00146 * .. 00147 * .. Executable Statements .. 00148 * 00149 * Get grid parameters 00150 * 00151 CALL BLACS_GRIDINFO( ICTXT, NPROW, NPCOL, MYROW, MYCOL ) 00152 * 00153 INFO = 0 00154 IF( M.LT.0 ) THEN 00155 INFO = -2 00156 ELSE IF( N.LT.0 ) THEN 00157 INFO = -3 00158 ELSE IF( MB.LT.1 ) THEN 00159 INFO = -4 00160 ELSE IF( NB.LT.1 ) THEN 00161 INFO = -5 00162 ELSE IF( IRSRC.LT.0 .OR. IRSRC.GE.NPROW ) THEN 00163 INFO = -6 00164 ELSE IF( ICSRC.LT.0 .OR. ICSRC.GE.NPCOL ) THEN 00165 INFO = -7 00166 ELSE IF( NPROW.EQ.-1 ) THEN 00167 INFO = -8 00168 ELSE IF( LLD.LT.MAX( 1, NUMROC( M, MB, MYROW, IRSRC, 00169 $ NPROW ) ) ) THEN 00170 INFO = -9 00171 END IF 00172 * 00173 IF( INFO.NE.0 ) 00174 $ CALL PXERBLA( ICTXT, 'DESCINIT', -INFO ) 00175 * 00176 DESC( DTYPE_ ) = BLOCK_CYCLIC_2D 00177 DESC( M_ ) = MAX( 0, M ) 00178 DESC( N_ ) = MAX( 0, N ) 00179 DESC( MB_ ) = MAX( 1, MB ) 00180 DESC( NB_ ) = MAX( 1, NB ) 00181 DESC( RSRC_ ) = MAX( 0, MIN( IRSRC, NPROW-1 ) ) 00182 DESC( CSRC_ ) = MAX( 0, MIN( ICSRC, NPCOL-1 ) ) 00183 DESC( CTXT_ ) = ICTXT 00184 DESC( LLD_ ) = MAX( LLD, MAX( 1, NUMROC( DESC( M_ ), DESC( MB_ ), 00185 $ MYROW, DESC( RSRC_ ), NPROW ) ) ) 00186 * 00187 RETURN 00188 * 00189 * End DESCINIT 00190 * 00191 END
