?laqhb

Developer Reference for Intel® oneAPI Math Kernel Library for Fortran

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ID 766686

Date 3/31/2023

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?laqhb

Scales a Hermetian band matrix, using scaling factors computed by ?pbequ.

Syntax

call claqhb( uplo, n, kd, ab, ldab, s, scond, amax, equed )

call zlaqhb( uplo, n, kd, ab, ldab, s, scond, amax, equed )

Include Files

mkl.fi

Description

The routine equilibrates a Hermetian band matrix A using the scaling factors in the vector s.

Input Parameters

uplo

CHARACTER*1.

Specifies whether the upper or lower triangular part of the band matrix A is stored.

If uplo = 'U': upper triangular.

If uplo = 'L': lower triangular.

n

INTEGER. The order of the matrix A.

n≥ 0.

kd

INTEGER. The number of super-diagonals of the matrix A if uplo = 'U', or the number of sub-diagonals if uplo = 'L'.

kd≥ 0.

ab

COMPLEX for claqhb

DOUBLE COMPLEX for zlaqhb

Array, DIMENSION (ldab,n). On entry, the upper or lower triangle of the band matrix A, stored in the first kd+1 rows of the array. The j-th column of A is stored in the j-th column of the array ab as follows:

if uplo = 'U', ab(kd+1+i-j,j) = A(i,j) for max(1,j-kd) ≤ i ≤ j;

if uplo = 'L', ab(1+i-j,j) = A(i,j) for j ≤ i ≤ min(n,j+kd).

ldab

INTEGER. The leading dimension of the array ab.

ldab≥kd+1.

scond

REAL for claqsb

DOUBLE PRECISION for zlaqsb

Ratio of the smallest s(i) to the largest s(i).

amax

REAL for claqsb

DOUBLE PRECISION for zlaqsb

Absolute value of largest matrix entry.

Output Parameters

ab

On exit, if info = 0, the triangular factor U or L from the Cholesky factorization A = U^H*U or A = L*L^H of the band matrix A, in the same storage format as A.

s

REAL for claqsb

DOUBLE PRECISION for zlaqsb

Array, DIMENSION (n). The scale factors for A.

equed

CHARACTER*1.

Specifies whether or not equilibration was done.

If equed = 'N': No equilibration.

If equed = 'Y': Equilibration was done, that is, A has been replaced by diag(s)*A*diag(s).

Application Notes

The routine uses internal parameters thresh, large, and small, which have the following meaning. thresh is a threshold value used to decide if scaling should be based on the ratio of the scaling factors. If scond < thresh, scaling is done.

The values large and small are threshold values used to decide if scaling should be done based on the absolute size of the largest matrix element. If amax > large or amax < small, scaling is done.

Parent topic: LAPACK Auxiliary Routines

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Developer Reference for Intel® oneAPI Math Kernel Library for Fortran

?laqhb