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💖 NAME 💖

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

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✨ SYNOPSIS ✨

🌸 Functions/Subroutines 🌸

• subroutine DLA_SYAMV (uplo, n, alpha, a, lda, x, incx, beta, y, incy) — DLA_SYAMV computes a matrix-vector product using a symmetric indefinite matrix to calculate error bounds.

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🦋 Function/Subroutine Documentation 🦋

💜 subroutine DLA_SYAMV 💜

subroutine DLA_SYAMV (integer uplo, integer n, double precision alpha, double precision, dimension( lda, * ) a, integer lda, double precision, dimension( * ) x, integer incx, double precision beta, double precision, dimension( * ) y, integer incy)

DLA_SYAMV computes a matrix-vector product using a symmetric indefinite matrix to calculate error bounds.

🎀 Purpose 🎀

DLA_SYAMV performs the matrix-vector operation

y := alpha*abs(A)*abs(x) + beta*abs(y),

where alpha and beta are scalars, x and y are vectors and A is an n by n symmetric 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.

🍓 Parameters 🍓

• UPLO — UPLO is INTEGER. On entry, UPLO specifies whether the upper or lower triangular part of the array A is to be referenced as follows:
  • UPLO = BLAS_UPPER — only the upper triangular part of A is to be referenced.
  • UPLO = BLAS_LOWER — only the lower triangular part of A is to be referenced.

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.
• ALPHA — ALPHA is DOUBLE PRECISION . On entry, ALPHA specifies the scalar alpha. Unchanged on exit.
• A — A is DOUBLE PRECISION array, dimension ( LDA, n ). Before entry, the leading m by n part of the array A must contain the matrix of coefficients. Unchanged on exit.
• 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 ). Unchanged on exit.
• X — X is DOUBLE PRECISION array, dimension ( 1 + ( n - 1 )*abs( INCX ) ). 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 DOUBLE PRECISION . 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 DOUBLE PRECISION array, dimension ( 1 + ( n - 1 )*abs( INCY ) ). 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.
• INCY — INCY is INTEGER. On entry, INCY specifies the increment for the elements of Y. INCY must not be zero. Unchanged on exit.

👑 Author 👑

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

🔥 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.
• -- Modified for the absolute-value product, April 2006
  • Jason Riedy, UC Berkeley

Definition at line 175 of file dla_syamv.f.

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🌈 Author 🌈

Generated automatically by Doxygen for LAPACK from the source code.

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