?sytri2x

Developer Reference for Intel® oneAPI Math Kernel Library for Fortran

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ID 766686

Date 3/31/2023

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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*U^T or A = L*D*L^T 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	CHARACTER1. Must be 'U' or 'L'. Indicates how the input matrix `A` has been factored: If `uplo = 'U'`, the array `a` stores the factorization `A = UDU^T`. If `uplo = 'L'`, the array `a` stores the factorization `A = LD*L^T`.
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

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.

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'.

Parent topic: Matrix Inversion: LAPACK Computational Routines

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