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HPL_pdrpancrT(3) HPL Library Functions HPL_pdrpancrT(3)## NAME

HPL_pdrpancrT - Crout recursive panel factorization.## SYNOPSIS

#include"hpl.h"voidHPL_pdrpancrT(HPL_T_panel*PANEL,constintM,constintN,constintICOFF,double*WORK);## DESCRIPTION

HPL_pdrpancrTrecursively factorizes a panel of columns using the recursive Crout variant of the usual one-dimensional algorithm. The lower triangular N0-by-N0 upper block of the panel is stored in transpose form. Bi-directional exchange is used to perform the swap::broadcast operations at once for one column in the panel. This results in a lower number of slightly larger messages than usual. On P processes and assuming bi-directional links, the running time of this function can be approximated by (when N is equal to N0): N0 * log_2( P ) * ( lat + ( 2*N0 + 4 ) / bdwth ) + N0^2 * ( M - N0/3 ) * gam2-3 where M is the local number of rows of the panel, lat and bdwth are the latency and bandwidth of the network for double precision real words, and gam2-3 is an estimate of the Level 2 and Level 3 BLAS rate of execution. The recursive algorithm allows indeed to almost achieve Level 3 BLAS performance in the panel factorization. On a large number of modern machines, this operation is however latency bound, meaning that its cost can be estimated by only the latency portion N0 * log_2(P) * lat. Mono-directional links will double this communication cost.## ARGUMENTS

PANEL (local input/output) HPL_T_panel * On entry, PANEL points to the data structure containing the panel information. M (local input) const int On entry, M specifies the local number of rows of sub(A). N (local input) const int On entry, N specifies the local number of columns of sub(A). ICOFF (global input) const int On entry, ICOFF specifies the row and column offset of sub(A) in A. WORK (local workspace) double * On entry, WORK is a workarray of size at least 2*(4+2*N0).## SEE ALSO

HPL_dlocmax(3),HPL_dlocswpN(3),HPL_dlocswpT(3),HPL_pdmxswp(3),HPL_pdpancrN(3),HPL_pdpancrT(3),HPL_pdpanllN(3),HPL_pdpanllT(3),HPL_pdpanrlN(3),HPL_pdpanrlT(3),HPL_pdrpancrN(3),HPL_pdrpanllN(3),HPL_pdrpanllT(3),HPL_pdrpanrlN(3),HPL_pdrpanrlT(3),HPL_pdfact(3). HPL 2.1 October 26, 2012 HPL_pdrpancrT(3)

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