
dsbmv.f(3) LAPACK dsbmv.f(3)
NAME
dsbmv.f 
SYNOPSIS
Functions/Subroutines
subroutine dsbmv (UPLO, N, K, ALPHA, A, LDA, X, INCX, BETA, Y, INCY)
DSBMV
Function/Subroutine Documentation
subroutine dsbmv (characterUPLO, integerN, integerK, double precisionALPHA, double precision,
dimension(lda,*)A, integerLDA, double precision, dimension(*)X, integerINCX, double
precisionBETA, double precision, dimension(*)Y, integerINCY)
DSBMV Purpose:
DSBMV performs the matrixvector operation
y := alpha*A*x + beta*y,
where alpha and beta are scalars, x and y are n element vectors and
A is an n by n symmetric band matrix, with k superdiagonals.
Parameters:
UPLO
UPLO is CHARACTER*1
On entry, UPLO specifies whether the upper or lower
triangular part of the band matrix A is being supplied as
follows:
UPLO = 'U' or 'u' The upper triangular part of A is
being supplied.
UPLO = 'L' or 'l' The lower triangular part of A is
being supplied.
N
N is INTEGER
On entry, N specifies the order of the matrix A.
N must be at least zero.
K
K is INTEGER
On entry, K specifies the number of superdiagonals of the
matrix A. K must satisfy 0 .le. K.
ALPHA
ALPHA is DOUBLE PRECISION.
On entry, ALPHA specifies the scalar alpha.
A
A is DOUBLE PRECISION array of DIMENSION ( LDA, n ).
Before entry with UPLO = 'U' or 'u', the leading ( k + 1 )
by n part of the array A must contain the upper triangular
band part of the symmetric matrix, supplied column by
column, with the leading diagonal of the matrix in row
( k + 1 ) of the array, the first superdiagonal starting at
position 2 in row k, and so on. The top left k by k triangle
of the array A is not referenced.
The following program segment will transfer the upper
triangular part of a symmetric band matrix from conventional
full matrix storage to band storage:
DO 20, J = 1, N
M = K + 1  J
DO 10, I = MAX( 1, J  K ), J
A( M + I, J ) = matrix( I, J )
10 CONTINUE
20 CONTINUE
Before entry with UPLO = 'L' or 'l', the leading ( k + 1 )
by n part of the array A must contain the lower triangular
band part of the symmetric matrix, supplied column by
column, with the leading diagonal of the matrix in row 1 of
the array, the first subdiagonal starting at position 1 in
row 2, and so on. The bottom right k by k triangle of the
array A is not referenced.
The following program segment will transfer the lower
triangular part of a symmetric band matrix from conventional
full matrix storage to band storage:
DO 20, J = 1, N
M = 1  J
DO 10, I = J, MIN( N, J + K )
A( M + I, J ) = matrix( I, J )
10 CONTINUE
20 CONTINUE
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
( k + 1 ).
X
X is DOUBLE PRECISION array of DIMENSION at least
( 1 + ( n  1 )*abs( INCX ) ).
Before entry, the incremented array X must contain the
vector x.
INCX
INCX is INTEGER
On entry, INCX specifies the increment for the elements of
X. INCX must not be zero.
BETA
BETA is DOUBLE PRECISION.
On entry, BETA specifies the scalar beta.
Y
Y is DOUBLE PRECISION array of DIMENSION at least
( 1 + ( n  1 )*abs( INCY ) ).
Before entry, 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.
Author:
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
November 2011
Further Details:
Level 2 Blas routine.
The vector and matrix arguments are not referenced when N = 0, or M = 0
 Written on 22October1986.
Jack Dongarra, Argonne National Lab.
Jeremy Du Croz, Nag Central Office.
Sven Hammarling, Nag Central Office.
Richard Hanson, Sandia National Labs.
Definition at line 185 of file dsbmv.f.
Author
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Version 3.4.2 Tue Sep 25 2012 dsbmv.f(3) 
