SRC/cla_gbamv.f(3)

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version 3.12.1 · 7 versions
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💖 SRC/cla_gbamv.f(3) 💖

okay so bestie, this is the Library Functions Manual page for SRC/cla_gbamv.f — yes we're doing LAPACK/BLAS math and we're doing it with sparkle 💅✨

🌸 NAME 🌸

SRC/cla_gbamv.f — that's the page name, and it's all about the cla_gbamv subroutine 🫶

✨ SYNOPSIS ✨

🧚 Functions/Subroutines 🧚

  • subroutine cla_gbamv — CLA_GBAMV performs a matrix-vector operation to calculate error bounds.
       subroutine cla_gbamv (trans, m, n, kl, ku, alpha, ab, ldab, x, incx,
           beta, y, incy)

🔥 Function/Subroutine Documentation 🔥

🌸 subroutine cla_gbamv 🌸

Here's the full signature, copied exactly so nobody comes for me 😭

   subroutine cla_gbamv (integer trans, integer m, integer n, integer kl,
       integer ku, real alpha, complex, dimension( ldab, * ) ab, integer ldab,
       complex, dimension( * ) x, integer incx, real beta, real, dimension( * )
       y, integer incy)

CLA_GBAMV performs a matrix-vector operation to calculate error bounds. Iconic. 👑

🎀 Purpose 🎀

Okay so CLA_GBAMV performs one of these matrix-vector operations, literally:

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. periodt 🦋

🌈 Parameters 🌈

  • TRANS — TRANS is INTEGER. On entry, TRANS specifies the operation to be performed as follows:
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, M specifies the number of rows of the matrix A. M must be at least zero. Unchanged on exit.
  • N — N is INTEGER. On entry, N specifies the number of columns of the matrix A. N must be at least zero. Unchanged on exit.
  • KL — KL is INTEGER. The number of subdiagonals within the band of A. KL >= 0.
  • KU — KU is INTEGER. The number of superdiagonals within the band of A. KU >= 0.
  • ALPHA — ALPHA is REAL. On entry, ALPHA specifies the scalar alpha. Unchanged on exit.
  • AB — AB is COMPLEX array, dimension (LDAB,n). Before entry, the leading m by n part of the array AB must contain the matrix of coefficients. Unchanged on exit.
  • LDAB — LDAB is INTEGER. On entry, LDAB specifies the first dimension of AB as declared in the calling (sub) program. LDAB must be at least max( 1, m ). Unchanged on exit.
  • X — X is COMPLEX 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, INCX specifies the increment for the elements of X. INCX must not be zero. Unchanged on exit.
  • BETA — BETA is REAL. On entry, BETA specifies the scalar beta. When BETA is supplied as zero then Y need not be set on input. Unchanged on exit.
  • Y — Y is REAL array, dimension ( 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, INCY specifies the increment for the elements of Y. INCY must not be zero. Unchanged on exit.

Level 2 Blas routine.

👑 Author 👑

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

Definition at line 186 of file cla_gbamv.f.

👑 Author 👑

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This page is from LAPACK Version 3.12.0, page SRC/cla_gbamv.f(3) — the footer didn't print a date, so I'm not making one up, bestie periodt 💖✨

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