Developer Reference for Intel® oneAPI Math Kernel Library for Fortran

ID 766686
Date 11/07/2023
Public

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?sytri2x

Computes the inverse of a symmetric indefinite matrix after ?sytri2sets the leading dimension of the workspace.

Syntax

call ssytri2x( uplo, n, a, lda, ipiv, work, nb, info )

call dsytri2x( uplo, n, a, lda, ipiv, work, nb, info )

call csytri2x( uplo, n, a, lda, ipiv, work, nb, info )

call zsytri2x( uplo, n, a, lda, ipiv, work, nb, info )

call sytri2x( a,ipiv,nb[,uplo][,info] )

Include Files

  • mkl.fi, lapack.f90

Description

The routine computes the inverse inv(A) of a symmetric indefinite matrix A using the factorization A = U*D*UT or A = L*D*LT computed by ?sytrf.

The ?sytri2x actually computes the inverse after the ?sytri2 routine sets the leading dimension of the workspace before calling ?sytri2x.

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*UT.

If uplo = 'L', the array a stores the factorization A = L*D*LT.

n

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

a, work

REAL for ssytri2x

DOUBLE PRECISION for dsytri2x

COMPLEX for csytri2x

DOUBLE COMPLEX for zsytri2x

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 ?sytrf.

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

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

where

nb is the block size as set by ?sytrf.

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 ?sytrf.

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, Dii= 0; D is singular and its inversion could not be computed.

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 sytri2x 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'.