STRTRI(3)

💅 STRTRI(3) — the one where we invert a triangular matrix, bestie

okay so before we even get into it, hi, welcome, this page lives at /home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/SRC/strtri.f and it's part of the LAPACK Library Functions Manual and honestly? she's iconic. Let's go. 🎀

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✨ SYNOPSIS ✨

Functions/Subroutines

subroutine STRTRI (uplo, diag, n, a, lda, info)

STRTRI — that's the whole vibe, that's the name, no notes. 💜

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🌸 Function/Subroutine Documentation 🌸

subroutine STRTRI (character uplo, character diag, integer n, real,
    dimension( lda, * ) a, integer lda, integer info)

STRTRI (yes, again, she contains multitudes 💅)

🦋 Purpose

okay so literally what she does:

!>
!> STRTRI computes the inverse of a real upper or lower triangular
!> matrix A.
!>
!> This is the Level 3 BLAS version of the algorithm.
!>

so yeah — inverse of a real upper-or-lower triangular matrix A, and she's the Level 3 BLAS version of the algorithm. no cap. ✨

🎀 Parameters

UPLO

!>          UPLO is CHARACTER*1
!>          = 'U':  A is upper triangular;
!>          = 'L':  A is lower triangular.
!>

• UPLO is CHARACTER*1 — which triangle are we even talking about, bestie:
  • 'U' — A is upper triangular 💖
  • 'L' — A is lower triangular 🫶

DIAG

!>          DIAG is CHARACTER*1
!>          = 'N':  A is non-unit triangular;
!>          = 'U':  A is unit triangular.
!>

• DIAG is CHARACTER*1 — is the diagonal doing the most or not:
  • 'N' — A is non-unit triangular, the diagonal is real and it's doing its job 😤
  • 'U' — A is unit triangular, diagonal is assumed to be 1, main character energy 🌟

N

!>          N is INTEGER
!>          The order of the matrix A.  N >= 0.
!>

• N is INTEGER — the order of the matrix A. and like, N >= 0, please. no negative-matrix nonsense here 🙈

A

!>          A is REAL array, dimension (LDA,N)
!>          On entry, the triangular matrix A.  If UPLO = 'U', the
!>          leading N-by-N upper triangular part of the array A contains
!>          the upper triangular matrix, and the strictly lower
!>          triangular part of A is not referenced.  If UPLO = 'L', the
!>          leading N-by-N lower triangular part of the array A contains
!>          the lower triangular matrix, and the strictly upper
!>          triangular part of A is not referenced.  If DIAG = 'U', the
!>          diagonal elements of A are also not referenced and are
!>          assumed to be 1.
!>          On exit, the (triangular) inverse of the original matrix, in
!>          the same storage format.
!>

• A is a REAL array, dimension (LDA,N). On entry it's the triangular matrix A, and the storage rules are giving very specific:
  • if UPLO = 'U' — the leading N-by-N upper triangular part of the array A holds the upper triangular matrix, and the strictly lower triangular part of A is not referenced, she's simply ignored 💀
  • if UPLO = 'L' — the leading N-by-N lower triangular part of the array A holds the lower triangular matrix, and the strictly upper triangular part of A is not referenced 🙈
  • if DIAG = 'U' — the diagonal elements of A are also not referenced and are assumed to be 1 ✨
• On exit — the array holds the (triangular) inverse of the original matrix, in the same storage format. slay. 💅

LDA

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

• LDA is INTEGER — the leading dimension of the array A, and the rule is LDA >= max(1,N). respect the constraint, bestie 🫶

INFO

!>          INFO is INTEGER
!>          = 0: successful exit
!>          < 0: if INFO = -i, the i-th argument had an illegal value
!>          > 0: if INFO = i, A(i,i) is exactly zero.  The triangular
!>               matrix is singular and its inverse can not be computed.
!>

• INFO is INTEGER — the vibe check at the end:
  • = 0 — successful exit, we ate, no crumbs 🌈
  • < 0 — if INFO = -i, the i-th argument had an illegal value 😭
  • > 0 — if INFO = i, A(i,i) is exactly zero. the triangular matrix is singular and its inverse can not be computed. that's it, that's the end, do not pass go 🚨

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👑 Author

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

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fr fr, STRTRI is defined at line 108 of file strtri.f. you're welcome, iykyk 🧚

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🌟 Author

Generated automatically by Doxygen for LAPACK from the source code. she was literally built by a robot and still turned out this cute, obsessed 💖

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and that's the page!! this little cutie is from LAPACK, Version 3.12.0, dated /home/abui...RC/strtri.f(3). mwah, bye bestie 💋✨🌸