?hetri2x

Developer Reference for Intel® oneAPI Math Kernel Library for Fortran

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ID 766686

Date 4/28/2026

Version

Public

?hetri2x

Computes the inverse of a Hermitian indefinite matrix after ?hetri2 sets the leading dimension of the workspace allocates memory .

Syntax

call chetri2x ( uplo , n , a , lda , ipiv , work , nb , info )

call zhetri2x ( uplo , n , a , lda , ipiv , work , nb , info )

call hetri2x ( a , ipiv , nb [ , uplo ] [ , info ] )

Include Files

mkl.fi , mkl_lapack.f90

Description

The routine computes the inverse inv(A) of a Hermitian indefinite matrix A using the factorization A = U*D*U^{H} or A = L*D*L^{H} computed by ?hetrf .

The ?hetri2x actually computes the inverse after the ?hetri2 routine sets the leading dimension of the workspace allocates memory before calling ?hetri2x .

Input Parameters

uplo

CHARACTER*1 . Must be ‘U’ or ‘L’ .

Indicates how the input matrix A has been factored:

If uplo = 'U' , the array a stores the factorization A = U*D*U^{H} .

If uplo = 'L' , the array a stores the factorization A = L*D*L^{H} .

n

INTEGER . The order of the matrix A ; n≥ 0 .

a , work

COMPLEX for chetri2x

DOUBLE COMPLEX for zhetri2x

Arrays:

a ( lda ,*) contains the nb (block size) diagonal matrix D and the multipliers used to obtain the factor U or L as returned by ?hetrf .

The second dimension of a must be at least max(1,n) .

work is a workspace array of the dimension (n+nb+1)*(nb+3)

where

nb is the block size as set by ?hetrf .

a

Arrays a contains the nb (block size) diagonal matrix D and the multipliers used to obtain the factor U or L as returned by ?hetrf .

lda

INTEGER . The leading dimension of a ; lda≥ max(1, n) .

ipiv

INTEGER .

Array, size at least max(1, n) .

Details of the interchanges and the nb structure of D as returned by ?hetrf .

nb

INTEGER . Block size.

Output Parameters

a

If info = 0, the symmetric inverse of the original matrix.

If info = ‘U’ , the upper triangular part of the inverse is formed and the part of A below the diagonal is not referenced.

If info = ‘L’ , the lower triangular part of the inverse is formed and the part of A above the diagonal is not referenced.

info

INTEGER .

If info = 0, the execution is successful.
If info = -i , the i- th parameter had an illegal value.
If info = i , D_{ii} = 0; D is singular and its inversion could not be computed.

Return Values

No return value, info is an Output Parameter.

LAPACK 95 Interface Notes

Routines in Fortran 95 interface have fewer arguments in the calling sequence than their FORTRAN 77 counterparts. For general conventions applied to skip redundant or reconstructible arguments, see LAPACK 95 Interface Conventions .

Specific details for the routine hetri2x interface are as follows:

a

Holds the matrix A of size ( n,n ).

ipiv

Holds the vector of length n .

nb

Holds the block size.

uplo

Indicates how the input matrix A has been factored. Must be ‘U’ or ‘L’ .

NOTE:

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Developer Reference for Intel® oneAPI Math Kernel Library for Fortran

?hetri2x

Syntax

Include Files

Description

Input Parameters

Output Parameters

Return Values

LAPACK 95 Interface Notes