# zgbmv

```ZGBMV(1)                         BLAS routine                         ZGBMV(1)

NAME
ZGBMV - performs one of the matrix-vector operations   y := alpha*A*x +
beta*y, or y := alpha*A'*x + beta*y, or   y := alpha*conjg( A' )*x +
beta*y,

SYNOPSIS
SUBROUTINE ZGBMV(TRANS,M,N,KL,KU,ALPHA,A,LDA,X,INCX,BETA,Y,INCY)

DOUBLE                                                       COMPLEX
ALPHA,BETA

INTEGER                                                      INCX,INCY,KL,KU,LDA,M,N

CHARACTER                                                    TRANS

DOUBLE                                                       COMPLEX
A(LDA,*),X(*),Y(*)

PURPOSE
ZGBMV  performs one of the matrix-vector operations

where alpha and beta are scalars, x and y are vectors and A is an m by
n band matrix, with kl sub-diagonals and ku super-diagonals.

ARGUMENTS
TRANS  - CHARACTER*1.
On entry, TRANS specifies the operation to be performed as
follows:

TRANS = 'N' or 'n'   y := alpha*A*x + beta*y.

TRANS = 'T' or 't'   y := alpha*A'*x + beta*y.

TRANS = 'C' or 'c'   y := alpha*conjg( A' )*x + beta*y.

Unchanged on exit.

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

N      - INTEGER.
On entry, N specifies the number of columns of the matrix A.  N
must be at least zero.  Unchanged on exit.

KL     - INTEGER.
On entry, KL specifies the number of sub-diagonals of the matrix
A. KL must satisfy  0 .le. KL.  Unchanged on exit.

KU     - INTEGER.
On entry, KU specifies the number of super-diagonals of the
matrix A. KU must satisfy  0 .le. KU.  Unchanged on exit.

ALPHA  - COMPLEX*16      .
On entry, ALPHA specifies the scalar alpha.  Unchanged on exit.

A      - COMPLEX*16       array of DIMENSION ( LDA, n ).
Before entry, the leading ( kl + ku + 1 ) by n part of the array
A must contain the matrix of coefficients, supplied column by
column, with the leading diagonal of the matrix in row ( ku + 1
) of the array, the first super-diagonal starting at position 2
in row ku, the first sub-diagonal starting at position 1 in row
( ku + 2 ), and so on.  Elements in the array A that do not
correspond to elements in the band matrix (such as the top left
ku by ku triangle) are not referenced.  The following program
segment will transfer a band matrix from conventional full
matrix storage to band storage:

DO 20, J = 1, N K = KU + 1 - J DO 10, I = MAX( 1, J - KU ), MIN(
M, J + KL ) A( K + I, J ) = matrix( I, J ) 10    CONTINUE 20
CONTINUE

Unchanged on exit.

LDA    - INTEGER.
On entry, LDA specifies the first dimension of A as declared in
the calling (sub) program. LDA must be at least ( kl + ku + 1 ).
Unchanged on exit.

X      - COMPLEX*16       array of DIMENSION at least
( 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   - INTEGER.
On entry, INCX specifies the increment for the elements of X.
INCX must not be zero.  Unchanged on exit.

BETA   - COMPLEX*16      .
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      - COMPLEX*16       array of DIMENSION at least
( 1 + ( m - 1 )*abs( INCY ) ) when TRANS = 'N' or 'n' and at
least ( 1 + ( n - 1 )*abs( INCY ) ) otherwise.  Before entry,
the incremented array Y must contain the vector y. On exit, Y is
overwritten by the updated vector y.

INCY   - INTEGER.
On entry, INCY specifies the increment for the elements of Y.
INCY must not be zero.  Unchanged on exit.

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.

BLAS routine                     November 2008                        ZGBMV(1)```