p?laconsb

Developer Reference for Intel® oneAPI Math Kernel Library for C

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ID 766684

Date 10/15/2026

Version

Public

p?laconsb

Looks for two consecutive small subdiagonal elements.

Syntax

void pslaconsb(const float *a, const MKL_INT *desca, const MKL_INT *i, const MKL_INT *l,
               MKL_INT *m, const float *h44, const float *h33, const float *h43h34,
               float *buf, const MKL_INT *lwork);

void pdlaconsb(const double *a, const MKL_INT *desca, const MKL_INT *i, const MKL_INT *l,
               MKL_INT *m, const double *h44, const double *h33, const double *h43h34,
               double *buf, const MKL_INT *lwork);

void pclaconsb(const MKL_Complex8 *a, const MKL_INT *desca, const MKL_INT *i,
               const MKL_INT *l, MKL_INT *m, const MKL_Complex8 *h44,
               const MKL_Complex8 *h33, const MKL_Complex8 *h43h34, MKL_Complex8 *buf,
               const MKL_INT *lwork);

void pzlaconsb(const MKL_Complex16 *a, const MKL_INT *desca, const MKL_INT *i,
               const MKL_INT *l, MKL_INT *m, const MKL_Complex16 *h44,
               const MKL_Complex16 *h33, const MKL_Complex16 *h43h34, MKL_Complex16 *buf,
               const MKL_INT *lwork);

Include Files

mkl_scalapack.h

Description

pslaconsb pdlaconsb pclaconsb pzlaconsb The p?laconsb routine function looks for two consecutive small subdiagonal elements by analyzing the effect of starting a double shift QR iteration given by h44 , h33 , and h43h34 to see if this process makes a subdiagonal negligible.

Input Parameters

a

(local)

DOUBLE PRECISION for pdlaconsb COMPLEX for pclaconsb DOUBLE COMPLEX for pzlaconsb

Array of size (lld_a,LOCc(n_a))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.

h44 , h33 , h43h34

(global).

DOUBLE PRECISION for pdlaconsb COMPLEX for pclaconsb DOUBLE COMPLEX for pzlaconsb These three values are for the double shift QR iteration.

lwork

(local)

This must be at least 7*ceil(ceil( (i-l)/mb_a )/lcm(nprow, npcol)) . Here lcm is the least common multiple and nprow*npcol is the logical grid size.

Output Parameters

m: (global). On exit, this yields the starting location of the QR double shift. This will satisfy: l ≤ m ≤ i -2.
buf: (local). REAL for pslaconsb DOUBLE PRECISION for pdlaconsb COMPLEX for pclaconsb DOUBLE COMPLEX for pzlaconsb Array of size lwork .

NOTE:

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Developer Reference for Intel® oneAPI Math Kernel Library for C

p?laconsb

Syntax

Include Files

Description

Input Parameters

Output Parameters