/home/abui...la_geamv.f(3)

🎀 NAME 🎀

Hey bestie! You’re on the sla_geamv.f(3) page from the Library Functions Manual, and the file it’s documenting is literally this whole absolute path:

/home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/SRC/sla_geamv.f

No cap, that’s the one 💖

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✨ SYNOPSIS ✨

Functions/Subroutines

       subroutine SLA_GEAMV (trans, m, n, alpha, a, lda, x, incx, beta, y,
           incy)
           SLA_GEAMV computes a matrix-vector product using a general matrix to
           calculate error bounds.

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🦋 Function/Subroutine Documentation 🦋

   subroutine SLA_GEAMV (integer trans, integer m, integer n, real alpha, real,
       dimension( lda, * ) a, integer lda, real, dimension( * ) x, integer
       incx, real beta, real, dimension( * ) y, integer incy)

SLA_GEAMV computes a matrix-vector product using a general matrix to calculate error bounds. Periodt. 💅

💫 Purpose 💫

!>
!> SLA_GEAMV  performs one of the matrix-vector operations
!>
!>         y := alpha*abs(A)*abs(x) + beta*abs(y),
!>    or   y := alpha*abs(A)**T*abs(x) + beta*abs(y),
!>
!> where alpha and beta are scalars, x and y are vectors and A is an
!> m by n matrix.
!>
!> This function is primarily used in calculating error bounds.
!> To protect against underflow during evaluation, components in
!> the resulting vector are perturbed away from zero by (N+1)
!> times the underflow threshold.  To prevent unnecessarily large
!> errors for block-structure embedded in general matrices,
!>  zero components are not perturbed.  A zero
!> entry is considered  if all multiplications involved
!> in computing that entry have at least one zero multiplicand.
!>

bestie, this is error-bound math, so the little underflow-protection detail is literally the whole point 🫶

🌸 Parameters 🌸

TRANS

TRANS is INTEGER. On entry, it picks which operation happens, like a little menu:

BLAS_NO_TRANS      y := alpha*abs(A)*abs(x) + beta*abs(y)
BLAS_TRANS         y := alpha*abs(A**T)*abs(x) + beta*abs(y)
BLAS_CONJ_TRANS    y := alpha*abs(A**T)*abs(x) + beta*abs(y)

Unchanged on exit. 💖

M

M is INTEGER. On entry, it’s the number of rows of the matrix A. M must be at least zero. Unchanged on exit.

N

N is INTEGER. On entry, it’s the number of columns of the matrix A. N must be at least zero. Unchanged on exit.

ALPHA

ALPHA is REAL. On entry, it’s the scalar alpha. Unchanged on exit.

A

A is a REAL array, dimension ( LDA, n ). Before entry, the leading m by n part of A must contain the matrix of coefficients. Unchanged on exit.

LDA

LDA is INTEGER. On entry, it’s the first dimension of A as declared in the calling (sub) program. LDA must be at least max( 1, m ). Unchanged on exit.

X

X is a REAL array, dimension ( 1 + ( n - 1 )*abs( INCX ) ) when TRANS = 'N' or 'n', and at least ( 1 + ( m - 1 )*abs( INCX ) ) otherwise. Before entry, the incremented array X must contain the vector x. Unchanged on exit.

INCX

INCX is INTEGER. On entry, it’s the increment for the elements of X. INCX must not be zero. Unchanged on exit.

BETA

BETA is REAL. On entry, it’s the scalar beta. When BETA is supplied as zero then Y need not be set on input. Unchanged on exit.

Y

Y is a REAL array, dimension at least ( 1 + ( m - 1 )*abs( INCY ) ) when TRANS = 'N' or 'n', and at least ( 1 + ( n - 1 )*abs( INCY ) ) otherwise. Before entry with BETA non-zero, the incremented array Y must contain the vector y. On exit, Y is overwritten by the updated vector y.

If either m or n is zero, then Y not referenced and the function performs a quick return. 🫶

INCY

INCY is INTEGER. On entry, it’s the increment for the elements of Y. INCY must not be zero. Unchanged on exit.

Level 2 Blas routine. ✨

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🌟 Author 🌟

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

Definition at line 174 of file sla_geamv.f.

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🫶 Author 🫶

Generated automatically by Doxygen for LAPACK from the source code.

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Cute sign-off time, bestie: the footer gives LAPACK Version 3.12.0 and the page path /home/abui...la_geamv.f(3) — that’s the source/version tea at the bottom, and the vibes are immaculate 💅✨