BLAS/SRC/strsv.f(3)

📦
version 3.12.1 · 4 versions
, in arch rolling

💅 BLAS/SRC/strsv.f(3) — Library Functions Manual ✨

okay bestie, settle in, because this is the BLAS/SRC/strsv.f page from the Library Functions Manual and it's literally the definition of "small but mighty" 🫶

🌸 NAME 🌸

BLAS/SRC/strsv.f — no cap, that's the whole name, that's the whole vibe 💖

✨ SYNOPSIS ✨

Functions/Subroutines

  • subroutine strsv (uplo, trans, diag, n, a, lda, x, incx) — STRSV 👑

🦋 Function/Subroutine Documentation 🦋

subroutine strsv (character uplo, character trans, character diag, integer
    n, real, dimension(lda,*) a, integer lda, real, dimension(*) x, integer
    incx)

STRSV 🎀

🎯 Purpose:

!>
!> STRSV  solves one of the systems of equations
!>
!>    A*x = b,   or   A**T*x = b,
!>
!> where b and x are n element vectors and A is an n by n unit, or
!> non-unit, upper or lower triangular matrix.
!>
!> No test for singularity or near-singularity is included in this
!> routine. Such tests must be performed before calling this routine.
!>

so basically: give it a triangular matrix A and a right-hand side vector b, and it hands you back x. iconic behaviour, honestly 💅

⚠️ big heads-up bestie: this routine does not check whether your matrix is singular or near-singular. zero vibe checks included. you gotta do those tests yourself before you call it, fr fr 😭

💜 Parameters 💜

  • UPLO — UPLO is CHARACTER*1. on entry, UPLO tells us whether the matrix is an upper or lower triangular matrix, like:
!>              UPLO = 'U' or 'u'   A is an upper triangular matrix.
!>
!>              UPLO = 'L' or 'l'   A is a lower triangular matrix.
  • TRANS — TRANS is CHARACTER*1. on entry, TRANS says which equations we're solving, and it's giving options:
!>              TRANS = 'N' or 'n'   A*x = b.
!>
!>              TRANS = 'T' or 't'   A**T*x = b.
!>
!>              TRANS = 'C' or 'c'   A**T*x = b.

(yes, 'T' and 'C' do the exact same thing here — they're twins, not that deep 💀)

  • DIAG — DIAG is CHARACTER*1. on entry, DIAG specifies whether or not A is unit triangular:
!>              DIAG = 'U' or 'u'   A is assumed to be unit triangular.
!>
!>              DIAG = 'N' or 'n'   A is not assumed to be unit
!>                                  triangular.
  • N — N is INTEGER. on entry, N specifies the order of the matrix A. N must be at least zero. (zero is allowed, we love an inclusive queen 🌈)
  • A — A is REAL array, dimension ( LDA, N ). okay so listen:
!>           Before entry with  UPLO = 'U' or 'u', the leading n by n
!>           upper triangular part of the array A must contain the upper
!>           triangular matrix and the strictly lower triangular part of
!>           A is not referenced.
!>           Before entry with UPLO = 'L' or 'l', the leading n by n
!>           lower triangular part of the array A must contain the lower
!>           triangular matrix and the strictly upper triangular part of
!>           A is not referenced.
!>           Note that when  DIAG = 'U' or 'u', the diagonal elements of
!>           A are not referenced either, but are assumed to be unity.

so half of your array is main character and the other half is literally not even invited to the party 🙈 and if DIAG = 'U'/'u', the diagonal also gets ghosted — it's assumed to be unity.

  • LDA — LDA is INTEGER. on entry, LDA specifies the first dimension of A as declared in the calling (sub) program. LDA must be at least max( 1, n ). 📏
  • X — X is REAL array, dimension at least ( 1 + ( n - 1 )*abs( INCX ) ). before entry, the incremented array X must contain the n element right-hand side vector b. on exit, X is overwritten with the solution vector x. 🎀 so yeah, it's an in-place glow-up: b goes in, x comes out, the original b is gone, don't come for me 😭
  • INCX — INCX is INTEGER. on entry, INCX specifies the increment for the elements of X. INCX must not be zero. periodt, zero is not allowed 🚫

👑 Author 👑

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

the whole squad showed up for this one 🫶

⭐ Further Details: ⭐

!>
!>  Level 2 Blas routine.
!>
!>  -- Written on 22-October-1986.
!>     Jack Dongarra, Argonne National Lab.
!>     Jeremy Du Croz, Nag Central Office.
!>     Sven Hammarling, Nag Central Office.
!>     Richard Hanson, Sandia National Labs.
!>

Level 2 BLAS routine, written on 22-October-1986 and still serving looks 🔥 the way this routine has been iconic since before most of us were born is genuinely unreal.

🍓 Definition 🍓

Definition at line 148 of file strsv.f. 📍

🌟 Author 🌟

Generated automatically by Doxygen for LAPACK from the source code. (not a human, just a very efficient little robot 🤖✨)

and that's the whole page bestie!! 💖 this came straight from LAPACK, Version 3.12.0, on BLAS/SRC/strsv.f(3) — go forth and solve those triangular systems, you absolute icon 💅👑🌈

📦 where this page comes from