1HPL_pipid(3) HPL Library Functions HPL_pipid(3)
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6 HPL_pipid - Simplify the pivot vector.
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9 #include "hpl.h"
10 void HPL_pipid( HPL_T_panel * PANEL, int * K, int * IPID );
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14 HPL_pipid computes an array IPID that contains the source and final
15 destination of matrix rows resulting from the application of N
16 interchanges as computed by the LU factorization with row partial
17 pivoting. The array IPID is such that the row of global index IPID(i)
18 should be mapped onto the row of global index IPID(i+1). Note that we
19 cannot really know the length of IPID a priori. However, we know that
20 this array is at least 2*N long, since there are N rows to swap and
21 broadcast. The length of this array must be smaller than or equal to
22 4*N, since every row is swapped with at most a single distinct remote
23 row. The algorithm constructing IPID goes as follows: Let IA be the
24 global index of the first row to be swapped.
25 For every row src IA + i with i in [0..N) to be swapped with row dst
27 such that dst is given by DPIV[i]:
28 Is row src the destination of a previous row of the current block,
30 that is, is there k odd such that IPID(k) is equal to src ?
31 Yes: update this destination with dst. For example, if the
32 pivot array is (0,2)(1,1)(2,5) ... , then when we swap rows 2 and 5,
33 we swap in fact row 0 and 5, i.e., row 0 goes to 5 and not 2 as it
34 was thought so far ...
35 No : add the pair (src,dst) at the end of IPID; row src has not
36 been moved yet.
37 Is row dst different from src the destination of a previous row of
39 the current block, i.e., is there k odd such that IPID(k) is equal to
40 dst ?
41 Yes: update IPID(k) with src. For example, if the pivot array
42 is (0,5)(1,1)(2,5) ... , then when we swap rows 2 and 5, we swap in
43 fact row 2 and 0, i.e., row 0 goes to 2 and not 5 as it was thought
44 so far ...
45 No : add the pair (dst,src) at the end of IPID; row dst has not
46 been moved yet.
47 Note that when src is equal to dst, the pair (dst,src) should not be
49 added to IPID in order to avoid duplicated entries in this array.
50 During the construction of the array IPID, we make sure that the
51 first N entries are such that IPID(k) with k odd is equal to IA+k/2.
52 For k in [0..K/2), the row of global index IPID(2*k) should be
53 mapped onto the row of global index IPID(2*k+1).
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56 PANEL (local input/output) HPL_T_panel *
57 On entry, PANEL points to the data structure containing the
58 panel information.
59 K (global output) int *
61 On exit, K specifies the number of entries in IPID. K is at
62 least 2*N, and at most 4*N.
63 IPID (global output) int *
65 On entry, IPID is an array of length 4*N. On exit, the first K
66 entries of that array contain the src and final destination
67 resulting from the application of the N interchanges as
68 specified by DPIV. The pairs (src,dst) are contiguously
69 stored and sorted so that IPID(2*i+1) is equal to IA+i with i
70 in [0..N)
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73 HPL_pdlaswp00N (3), HPL_pdlaswp00T (3), HPL_pdlaswp01N (3),
74 HPL_pdlaswp01T (3).
75HPL 2.1 October 26, 2012 HPL_pipid(3)