SRC/dtrtri.f(3)

✨ SRC/dtrtri.f ✨

okay so this is the dtrtri page from the LAPACK manual, bestie — like, the whole thing, every single detail, no cap 💅

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🎀 SYNOPSIS 🎀

Functions/Subroutines

• subroutine dtrtri (uplo, diag, n, a, lda, info) — DTRTRI 💖

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🦋 Function/Subroutine Documentation 🦋

subroutine dtrtri (character uplo, character diag, integer n, double precision, dimension( lda, * ) a, integer lda, integer info)

DTRTRI

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🌸 Purpose:

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

so basically it inverts a real triangular matrix for you, and it's the Level 3 BLAS version of the algorithm — that's the whole vibe 🔥

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💜 Parameters

UPLO

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

• '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.
!>

• 'N' — A is non-unit triangular
• 'U' — A is unit triangular (iykyk)

N

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

the order of the matrix A, and it has to be N >= 0 ✨

A

!>          A is DOUBLE PRECISION 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.
!>

okay this one's the main character 😭 — A is a DOUBLE PRECISION array, dimension (LDA,N).

• On entry it's the triangular matrix A. 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. 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. And if DIAG = 'U', the diagonal elements of A are also not referenced and are assumed to be 1 🙈
• On exit you get the (triangular) inverse of the original matrix, in the same storage format 💖

LDA

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

the leading dimension of the array A, and it's gotta be LDA >= max(1,N) ⭐

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.
!>

• = 0 — successful exit, we ate 💅
• < 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 💀

bestie fr fr: that > 0 case is the jump-scare. singular matrix = no inverse = no vibes. check your INFO 🚨

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🌈 Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

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Definition at line 108 of file dtrtri.f. 🎀

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💫 Author (the meta one) 💫

Generated automatically by Doxygen for LAPACK from the source code. not me being auto-generated 😭

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okay that's the whole page, no notes 🫶 this lil doc is from LAPACK, Version 3.12.0, and it's the SRC/dtrtri.f(3) page — mwah, go invert something triangular responsibly 💖✨🍓