root / www / HPL_pdfact.html @ 8
Historique | Voir | Annoter | Télécharger (3,04 ko)
| 1 |
<HTML>
|
|---|---|
| 2 |
<HEAD>
|
| 3 |
<TITLE>HPL_pdfact HPL 2.0 Library Functions September 10, 2008</TITLE> |
| 4 |
</HEAD>
|
| 5 |
|
| 6 |
<BODY BGCOLOR="WHITE" TEXT = "#000000" LINK = "#0000ff" VLINK = "#000099" |
| 7 |
ALINK = "#ffff00"> |
| 8 |
|
| 9 |
<H1>Name</H1> |
| 10 |
<B>HPL_pdfact</B> recursive panel factorization. |
| 11 |
|
| 12 |
<H1>Synopsis</H1> |
| 13 |
<CODE>#include "hpl.h"</CODE><BR><BR> |
| 14 |
<CODE>void</CODE> |
| 15 |
<CODE>HPL_pdfact(</CODE> |
| 16 |
<CODE>HPL_T_panel *</CODE> |
| 17 |
<CODE>PANEL</CODE> |
| 18 |
<CODE>);</CODE> |
| 19 |
|
| 20 |
<H1>Description</H1> |
| 21 |
<B>HPL_pdfact</B> |
| 22 |
recursively factorizes a 1-dimensional panel of columns. |
| 23 |
The RPFACT function pointer specifies the recursive algorithm to be |
| 24 |
used, either Crout, Left- or Right looking. NBMIN allows to vary the |
| 25 |
recursive stopping criterium in terms of the number of columns in the |
| 26 |
panel, and NDIV allow to specify the number of subpanels each panel |
| 27 |
should be divided into. Usuallly a value of 2 will be chosen. Finally |
| 28 |
PFACT is a function pointer specifying the non-recursive algorithm to |
| 29 |
to be used on at most NBMIN columns. One can also choose here between |
| 30 |
Crout, Left- or Right looking. Empirical tests seem to indicate that |
| 31 |
values of 4 or 8 for NBMIN give the best results. |
| 32 |
|
| 33 |
Bi-directional exchange is used to perform the swap::broadcast |
| 34 |
operations at once for one column in the panel. This results in a |
| 35 |
lower number of slightly larger messages than usual. On P processes |
| 36 |
and assuming bi-directional links, the running time of this function |
| 37 |
can be approximated by (when N is equal to N0): |
| 38 |
|
| 39 |
N0 * log_2( P ) * ( lat + ( 2*N0 + 4 ) / bdwth ) + |
| 40 |
N0^2 * ( M - N0/3 ) * gam2-3 |
| 41 |
|
| 42 |
where M is the local number of rows of the panel, lat and bdwth are |
| 43 |
the latency and bandwidth of the network for double precision real |
| 44 |
words, and gam2-3 is an estimate of the Level 2 and Level 3 BLAS |
| 45 |
rate of execution. The recursive algorithm allows indeed to almost |
| 46 |
achieve Level 3 BLAS performance in the panel factorization. On a |
| 47 |
large number of modern machines, this operation is however latency |
| 48 |
bound, meaning that its cost can be estimated by only the latency |
| 49 |
portion N0 * log_2(P) * lat. Mono-directional links will double this |
| 50 |
communication cost. |
| 51 |
|
| 52 |
<H1>Arguments</H1> |
| 53 |
<PRE>
|
| 54 |
PANEL (local input/output) HPL_T_panel * |
| 55 |
On entry, PANEL points to the data structure containing the |
| 56 |
panel information. |
| 57 |
</PRE>
|
| 58 |
|
| 59 |
<H1>See Also</H1> |
| 60 |
<A HREF="HPL_dlocmax.html">HPL_dlocmax</A>, |
| 61 |
<A HREF="HPL_dlocswpN.html">HPL_dlocswpN</A>, |
| 62 |
<A HREF="HPL_dlocswpT.html">HPL_dlocswpT</A>, |
| 63 |
<A HREF="HPL_pdmxswp.html">HPL_pdmxswp</A>, |
| 64 |
<A HREF="HPL_pdpancrN.html">HPL_pdpancrN</A>, |
| 65 |
<A HREF="HPL_pdpancrT.html">HPL_pdpancrT</A>, |
| 66 |
<A HREF="HPL_pdpanllN.html">HPL_pdpanllN</A>, |
| 67 |
<A HREF="HPL_pdpanllT.html">HPL_pdpanllT</A>, |
| 68 |
<A HREF="HPL_pdpanrlN.html">HPL_pdpanrlN</A>, |
| 69 |
<A HREF="HPL_pdpanrlT.html">HPL_pdpanrlT</A>, |
| 70 |
<A HREF="HPL_pdrpancrN.html">HPL_pdrpancrN</A>, |
| 71 |
<A HREF="HPL_pdrpancrT.html">HPL_pdrpancrT</A>, |
| 72 |
<A HREF="HPL_pdrpanllN.html">HPL_pdrpanllN</A>, |
| 73 |
<A HREF="HPL_pdrpanllT.html">HPL_pdrpanllT</A>, |
| 74 |
<A HREF="HPL_pdrpanrlN.html">HPL_pdrpanrlN</A>, |
| 75 |
<A HREF="HPL_pdrpanrlT.html">HPL_pdrpanrlT</A>. |
| 76 |
|
| 77 |
</BODY>
|
| 78 |
</HTML>
|