SCALAPACK 2.2.2
LAPACK: Linear Algebra PACKage
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◆ PB_Cnumroc()

Int PB_Cnumroc ( Int  N,
Int  I,
Int  INB,
Int  NB,
Int  PROC,
Int  SRCPROC,
Int  NPROCS 
)

Definition at line 23 of file PB_Cnumroc.c.

29{
30/*
31* Purpose
32* =======
33*
34* PB_Cnumroc returns the local number of matrix rows/columns process
35* PROC will get if we give out N rows/columns starting from global in-
36* dex I.
37*
38* Arguments
39* =========
40*
41* N (global input) INTEGER
42* On entry, N specifies the number of rows/columns being dealt
43* out. N must be at least zero.
44*
45* I (global input) INTEGER
46* On entry, I specifies the global index of the matrix entry.
47* I must be at least zero.
48*
49* INB (global input) INTEGER
50* On entry, INB specifies the size of the first block of the
51* global matrix. INB must be at least one.
52*
53* NB (global input) INTEGER
54* On entry, NB specifies the size of the blocks used to parti-
55* tion the matrix. NB must be at least one.
56*
57* PROC (local input) INTEGER
58* On entry, PROC specifies the coordinate of the process whose
59* local portion is determined. PROC must be at least zero and
60* strictly less than NPROCS.
61*
62* SRCPROC (global input) INTEGER
63* On entry, SRCPROC specifies the coordinate of the process
64* that possesses the first row or column of the matrix. When
65* SRCPROC = -1, the data is not distributed but replicated,
66* otherwise SRCPROC must be at least zero and strictly less
67* than NPROCS.
68*
69* NPROCS (global input) INTEGER
70* On entry, NPROCS specifies the total number of process rows
71* or columns over which the matrix is distributed. NPROCS must
72* be at least one.
73*
74* -- Written on April 1, 1998 by
75* Antoine Petitet, University of Tennessee, Knoxville 37996, USA.
76*
77* ---------------------------------------------------------------------
78*/
79/*
80* .. Local Scalars ..
81*/
82 Int ilocblk, mydist, nblocks;
83/* ..
84* .. Executable Statements ..
85*
86*/
87 if( ( SRCPROC == -1 ) || ( NPROCS == 1 ) )
88/*
89* The data is not distributed, or there is just one process in this dimension
90* of the grid.
91*/
92 return( N );
93/*
94* Compute coordinate of process owning I and corresponding INB
95*/
96 if( ( INB -= I ) <= 0 )
97 {
98/*
99* I is not in the first block, find out which process has it and update the
100* size of first block
101*/
102 nblocks = (-INB) / NB + 1;
103 SRCPROC += nblocks;
104 SRCPROC -= ( SRCPROC / NPROCS ) * NPROCS;
105 INB += nblocks * NB;
106 }
107/*
108* Now everything is just like N, I=0, INB, NB, SRCPROC, NPROCS. The discussion
109* goes as follows: compute my distance from the source process so that within
110* this process coordinate system, the source process is the process such that
111* mydist = 0, or equivalently PROC == SRCPROC.
112*
113* Find out how many full blocks are globally (nblocks) and locally (ilocblk)
114* in those N entries. Then remark that
115*
116* when mydist < nblocks - ilocblk * NPROCS, I own ilocblk + 1 full blocks,
117* when mydist > nblocks - ilocblk * NPROCS, I own ilocblk full blocks,
118* when mydist = nblocks - ilocblk * NPROCS, either the last block is not full
119* and I own it, or the last block is full and I am the first process owning
120* only ilocblk full blocks.
121*/
122 if( PROC == SRCPROC )
123 {
124/*
125* I am the source process, i.e. I own I (mydist = 0). When N <= INB, the
126* answer is simply N.
127*/
128 if( N <= INB ) return( N );
129/*
130* Find out how many full blocks are globally (nblocks) and locally (ilocblk)
131* in those N entries.
132*/
133 nblocks = ( N - INB ) / NB + 1;
134/*
135* Since mydist = 0 and nblocks - ilocblk * NPROCS >= 0, there are only two
136* possible cases:
137*
138* 1) When mydist = nblocks - ilocblk * NPROCS = 0, that is NPROCS divides
139* the global number of full blocks, then the source process SRCPROC owns
140* one more block than the other processes; and N can be rewritten as
141* N = INB + (nblocks-1) * NB + LNB with LNB >= 0 size of the last block.
142* Similarly, the local value Np corresponding to N can be written as
143* Np = INB + (ilocblk-1) * NB + LNB = N + ( ilocblk-1 - (nblocks-1) )*NB.
144* Note that this case cannot happen when ilocblk is zero, since nblocks
145* is at least one.
146*
147* 2) mydist = 0 < nblocks - ilocblk * NPROCS, the source process only owns
148* full blocks, and therefore Np = INB + ilocblk * NB. Note that when
149* ilocblk is zero, Np is just INB.
150*/
151 if( nblocks < NPROCS ) return( INB );
152
153 ilocblk = nblocks / NPROCS;
154 return( ( nblocks - ilocblk * NPROCS ) ? INB + ilocblk * NB :
155 N + ( ilocblk - nblocks ) * NB );
156 }
157 else
158 {
159/*
160* I am not the source process. When N <= INB, the answer is simply 0.
161*/
162 if( N <= INB ) return( 0 );
163/*
164* Find out how many full blocks are globally (nblocks) and locally (ilocblk)
165* in those N entries
166*/
167 nblocks = ( N - INB ) / NB + 1;
168/*
169* Compute my distance from the source process so that within this process
170* coordinate system, the source process is the process such that mydist=0.
171*/
172 if( ( mydist = PROC - SRCPROC ) < 0 ) mydist += NPROCS;
173/*
174* When mydist < nblocks - ilocblk * NPROCS, I own ilocblk + 1 full blocks of
175* size NB since I am not the source process,
176*
177* when mydist > nblocks - ilocblk * NPROCS, I own ilocblk full blocks of
178* size NB since I am not the source process,
179*
180* when mydist = nblocks - ilocblk * NPROCS,
181* either the last block is not full and I own it, in which case
182* N = INB + (nblocks - 1)*NB + LNB with LNB the size of the last block
183* such that NB > LNB > 0; the local value Np corresponding to N is given
184* by Np = ilocblk * NB + LNB = N - INB + ( ilocblk - nblocks + 1 ) * NB;
185* or the last block is full and I am the first process owning only ilocblk
186* full blocks of size NB, that is N = INB + ( nblocks - 1 ) * NB and
187* Np = ilocblk * NB = N - INB + ( ilocblk - nblocks + 1 ) * NB.
188*/
189 if( nblocks < NPROCS )
190 return( ( mydist < nblocks ) ? NB : ( ( mydist > nblocks ) ? 0 :
191 N - INB + NB * ( 1 - nblocks ) ) );
192
193 ilocblk = nblocks / NPROCS;
194 mydist -= nblocks - ilocblk * NPROCS;
195 return( ( mydist < 0 ) ? ( ilocblk + 1 ) * NB :
196 ( ( mydist > 0 ) ? ilocblk * NB :
197 N - INB + NB * ( ilocblk - nblocks + 1 ) ) );
198 }
199/*
200* End of PB_Cnumroc
201*/
202}
Int
#define Int
Definition Bconfig.h:22