p?lasmsub

Developer Reference for Intel® oneAPI Math Kernel Library for C

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ID 766684

Date 12/16/2022

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p?lasmsub

Looks for a small subdiagonal element from the bottom of the matrix that it can safely set to zero.

Syntax

void pslasmsub (const float *a, const MKL_INT *desca, const MKL_INT *i, const MKL_INT *l, MKL_INT *k, const float *smlnum, float *buf, const MKL_INT *lwork );

void pdlasmsub (const double *a, const MKL_INT *desca, const MKL_INT *i, const MKL_INT *l, MKL_INT *k, const double *smlnum, double *buf, const MKL_INT *lwork );

void pclasmsub (const MKL_Complex8 *a , const MKL_INT *desca , const MKL_INT *i , const MKL_INT *l , MKL_INT *k , const float *smlnum , MKL_Complex8 *buf , const MKL_INT *lwork );

void pzlasmsub (const MKL_Complex16 *a , const MKL_INT *desca , const MKL_INT *i , const MKL_INT *l , MKL_INT *k , const double *smlnum , MKL_Complex16 *buf , const MKL_INT *lwork );

Include Files

mkl_scalapack.h

Description

The p?lasmsubfunction looks for a small subdiagonal element from the bottom of the matrix that it can safely set to zero. This function performs a global maximum and must be called by all processes.

Input Parameters

a

(local)

Array of size lld_a*LOCc(n_a).

On entry, the Hessenberg matrix whose tridiagonal part is being scanned. Unchanged on exit.

desca

(global and local)

Array of size dlen_. The array descriptor for the distributed matrix A.

i

(global)

The global location of the bottom of the unreduced submatrix of A. Unchanged on exit.

l

(global)

The global location of the top of the unreduced submatrix of A.

Unchanged on exit.

smlnum

(global)

On entry, a "small number" for the given matrix. Unchanged on exit. The machine-dependent constants for the stopping criterion.

lwork

(local)

This must be at least 2*ceil(ceil((i-l)/mb_a )/ lcm(nprow,npcol)). Here lcm is least common multiple and nprowxnpcol is the logical grid size.

Output Parameters

k

(global)

On exit, this yields the bottom portion of the unreduced submatrix. This will satisfy: l ≤ k ≤ i-1.

buf

(local).

Array of size lwork.

Application Notes

This routine parallelizes the code from ?lahqr that looks for a single small subdiagonal element.

Parent topic: ScaLAPACK Auxiliary Routines

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p?lasmsub

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