dla_gbamv-f(3)

dla_gbamv.f –

Synopsis

Functions/Subroutines

subroutine dla_gbamv (TRANS, M, N, KL, KU, ALPHA, AB, LDAB, X, INCX, BETA, Y, INCY)
DLA_GBAMV performs a matrix-vector operation to calculate error bounds.

Function/Subroutine Documentation

subroutine dla_gbamv (integerTRANS, integerM, integerN, integerKL, integerKU, double precisionALPHA, double precision, dimension( ldab, * )AB, integerLDAB, double precision, dimension( * )X, integerINCX, double precisionBETA, double precision, dimension( * )Y, integerINCY)

DLA_GBAMV performs a matrix-vector operation to calculate error bounds.

Purpose:

 DLA_GBAMV 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,
 "symbolically" zero components are not perturbed. A zero
 entry is considered "symbolic" if all multiplications involved
 in computing that entry have at least one zero multiplicand.

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

 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 is INTEGER
 The number of subdiagonals within the band of A. KL >= 0.

 KU is INTEGER
 The number of superdiagonals within the band of A. KU >= 0.

ALPHA

 ALPHA is DOUBLE PRECISION
 On entry, ALPHA specifies the scalar alpha.
 Unchanged on exit.

 AB is DOUBLE PRECISION array of 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, LDA 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 is DOUBLE PRECISION 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 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 is DOUBLE PRECISION 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.

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.

Date:

September 2012

Definition at line 185 of file dla_gbamv.f.

Author

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