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<TITLE>HPL_pipid HPL 2.0 Library Functions September 10, 2008</TITLE> |
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ALINK = "#ffff00"> |
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<H1>Name</H1> |
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<B>HPL_pipid</B> Simplify the pivot vector. |
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<H1>Synopsis</H1> |
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<CODE>#include "hpl.h"</CODE><BR><BR> |
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<CODE>void</CODE> |
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<CODE>HPL_pipid(</CODE> |
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<CODE>HPL_T_panel *</CODE> |
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<CODE>PANEL</CODE>, |
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<CODE>int *</CODE> |
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<CODE>K</CODE>, |
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<CODE>int *</CODE> |
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<CODE>IPID</CODE> |
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<CODE>);</CODE> |
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<H1>Description</H1> |
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<B>HPL_pipid</B> |
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computes an array IPID that contains the source and final |
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destination of matrix rows resulting from the application of N |
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interchanges as computed by the LU factorization with row partial |
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pivoting. The array IPID is such that the row of global index IPID(i) |
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should be mapped onto the row of global index IPID(i+1). Note that we |
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cannot really know the length of IPID a priori. However, we know that |
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this array is at least 2*N long, since there are N rows to swap and |
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broadcast. The length of this array must be smaller than or equal to |
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4*N, since every row is swapped with at most a single distinct remote |
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row. The algorithm constructing IPID goes as follows: Let IA be the |
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global index of the first row to be swapped. |
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For every row src IA + i with i in [0..N) to be swapped with row dst |
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such that dst is given by DPIV[i]: |
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Is row src the destination of a previous row of the current block, |
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that is, is there k odd such that IPID(k) is equal to src ? |
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Yes: update this destination with dst. For example, if the |
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pivot array is (0,2)(1,1)(2,5) ... , then when we swap rows 2 and 5, |
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we swap in fact row 0 and 5, i.e., row 0 goes to 5 and not 2 as it |
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was thought so far ... |
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No : add the pair (src,dst) at the end of IPID; row src has not |
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been moved yet. |
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Is row dst different from src the destination of a previous row of |
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the current block, i.e., is there k odd such that IPID(k) is equal to |
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dst ? |
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Yes: update IPID(k) with src. For example, if the pivot array |
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is (0,5)(1,1)(2,5) ... , then when we swap rows 2 and 5, we swap in |
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fact row 2 and 0, i.e., row 0 goes to 2 and not 5 as it was thought |
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so far ... |
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No : add the pair (dst,src) at the end of IPID; row dst has not |
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been moved yet. |
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Note that when src is equal to dst, the pair (dst,src) should not be |
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added to IPID in order to avoid duplicated entries in this array. |
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During the construction of the array IPID, we make sure that the |
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first N entries are such that IPID(k) with k odd is equal to IA+k/2. |
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For k in [0..K/2), the row of global index IPID(2*k) should be |
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mapped onto the row of global index IPID(2*k+1). |
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<H1>Arguments</H1> |
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<PRE>
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PANEL (local input/output) HPL_T_panel * |
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On entry, PANEL points to the data structure containing the |
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panel information. |
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</PRE>
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<PRE>
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K (global output) int * |
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On exit, K specifies the number of entries in IPID. K is at |
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least 2*N, and at most 4*N. |
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</PRE>
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<PRE>
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IPID (global output) int * |
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On entry, IPID is an array of length 4*N. On exit, the first |
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K entries of that array contain the src and final destination |
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resulting from the application of the N interchanges as |
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specified by DPIV. The pairs (src,dst) are contiguously |
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stored and sorted so that IPID(2*i+1) is equal to IA+i with i |
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in [0..N) |
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</PRE>
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<H1>See Also</H1> |
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<A HREF="HPL_pdlaswp00N.html">HPL_pdlaswp00N</A>, |
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<A HREF="HPL_pdlaswp00T.html">HPL_pdlaswp00T</A>, |
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<A HREF="HPL_pdlaswp01N.html">HPL_pdlaswp01N</A>, |
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<A HREF="HPL_pdlaswp01T.html">HPL_pdlaswp01T</A>. |
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