# HPL_plindx1 man page

HPL_plindx1 — Compute local swapping index arrays.

## Synopsis

**#include "hpl.h"****void HPL_plindx1( HPL_T_panel *** *PANEL*, **const int** *K*, **const int *** *IPID*, **int *** *IPA*, **int *** *LINDXA*, **int *** *LINDXAU*, **int *** *IPLEN*, **int *** *IPMAP*, **int *** *IPMAPM1*, **int *** *PERMU*, **int *** *IWORK* **);**

## Description

**HPL_plindx1** computes two local arrays LINDXA and LINDXAU containing the local source and final destination position resulting from the application of row interchanges. In addition, this function computes three arrays IPLEN, IPMAP and IPMAPM1 that contain the logarithmic mapping information for the spreading phase.

## Arguments

- PANEL (local input/output) HPL_T_panel *
- On entry, PANEL points to the data structure containing the panel information.
- K (global input) const int
- On entry, K specifies the number of entries in IPID. K is at least 2*N, and at most 4*N.
- IPID (global input) const int *
- On entry, IPID is an array of length K. The first K entries of that array contain the src and final destination resulting from the application of the interchanges.
- IPA (global output) int *
- On exit, IPA specifies the number of rows that the current process row has that either belong to U or should be swapped with remote rows of A.
- LINDXA (global output) int *
- On entry, LINDXA is an array of dimension 2*N. On exit, this array contains the local indexes of the rows of A I have that should be copied into U.
- LINDXAU (global output) int *
- On exit, LINDXAU is an array of dimension 2*N. On exit, this array contains the local destination information encoded as follows. If LINDXAU(k) >= 0, row LINDXA(k) of A is to be copied in U at position LINDXAU(k). Otherwise, row LINDXA(k) of A should be locally copied into A(-LINDXAU(k),:).
- IPLEN (global output) int *
- On entry, IPLEN is an array of dimension NPROW + 1. On exit, this array is such that IPLEN[i] is the number of rows of A in the processes before process IPMAP[i] after the sort with the convention that IPLEN[nprow] is the total number of rows of the panel. In other words IPLEN[i+1]-IPLEN[i] is the local number of rows of A that should be moved to the process IPMAP[i]. IPLEN is such that the number of rows of the source process row can be computed as IPLEN[1] - IPLEN[0], and the remaining entries of this array are sorted so that the quantities IPLEN[i+1] - IPLEN[i] are logarithmically sorted.
- IPMAP (global output) int *
- On entry, IPMAP is an array of dimension NPROW. On exit, this array contains the logarithmic mapping of the processes. In other words, IPMAP[myrow] is the corresponding sorted process coordinate.
- IPMAPM1 (global output) int *
- On entry, IPMAPM1 is an array of dimension NPROW. On exit, this array contains the inverse of the logarithmic mapping contained in IPMAP: IPMAPM1[ IPMAP[i] ] = i, for all i in [0.. NPROCS)
- PERMU (global output) int *
- On entry, PERMU is an array of dimension JB. On exit, PERMU contains a sequence of permutations, that should be applied in increasing order to permute in place the row panel U.
- IWORK (workspace) int *
- On entry, IWORK is a workarray of dimension 2*JB.

## See Also

**HPL_pdlaswp00N** (3), **HPL_pdlaswp00T** (3), **HPL_pdlaswp01N** (3), **HPL_pdlaswp01T** (3).