SRC/chetri.f(3)

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🎀 chetri — the LAPACK girlie page

Okay so this is the SRC/chetri.f(3) page from the Library Functions Manual, and it's literally all about the chetri subroutine. Buckle up, bestie 💖

💖 NAME

SRC/chetri.f — that's the name on the label, and the main character is the chetri subroutine. Periodt.

🌸 SYNOPSIS

Functions/Subroutines

subroutine chetri (uplo, n, a, lda, ipiv, work, info)
    CHETRI

🦋 Function/Subroutine Documentation

Here's the full signature so you can copy-paste it exactly, no cap:

subroutine chetri (character uplo, integer n, complex, dimension( lda, * )
       a, integer lda, integer, dimension( * ) ipiv, complex, dimension( * )
       work, integer info)
       CHETRI

✨ Purpose

Okay so here's the whole point: CHETRI computes the inverse of a complex Hermitian indefinite matrix A using the factorization A = U*D*U**H or A = L*D*L**H computed by CHETRF. That's the job, and it ate. 💅

💜 Parameters

UPLO

UPLO is CHARACTER*1 and it specifies whether the details of the factorization are stored as an upper or lower triangular matrix.

= 'U':  Upper triangular, form is A = U*D*U**H;
= 'L':  Lower triangular, form is A = L*D*L**H.

N

N is INTEGER — the order of the matrix A. And N >= 0, bestie.

A

A is COMPLEX array, dimension (LDA,N).

On entry, the block diagonal matrix D and the multipliers used to obtain the factor U or L as computed by CHETRF.

On exit, if INFO = 0, the (Hermitian) inverse of the original matrix. If UPLO = 'U', the upper triangular part of the inverse is formed and the part of A below the diagonal is not referenced; if UPLO = 'L' the lower triangular part of the inverse is formed and the part of A above the diagonal is not referenced.

LDA

LDA is INTEGER — the leading dimension of the array A. LDA >= max(1,N).

IPIV

IPIV is INTEGER array, dimension (N) — details of the interchanges and the block structure of D as determined by CHETRF.

WORK

WORK is COMPLEX array, dimension (N) — that's it, that's the whole description. 💀

INFO

INFO is INTEGER

  • = 0: successful exit
  • < 0: if INFO = -i, the i-th argument had an illegal value
  • > 0: if INFO = i, D(i,i) = 0; the matrix is singular and its inverse could not be computed.
Real talk: if INFO > 0, the matrix is singular and its inverse could not be computed. So don't try to manifest an inverse that isn't there, bestie. 😭

👑 Author

  • Univ. of Tennessee
  • Univ. of California Berkeley
  • Univ. of Colorado Denver
  • NAG Ltd.

Definition at line 113 of file chetri.f.

🤖 Author

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Bye bestie 💖 This cutie was served to you by LAPACK, Version 3.12.0, from SRC/chetri.f(3). Slay, go invert something safely. ✨🫶

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