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# chpmv

```
NAME
CHPMV - perform the matrix-vector operation   y := alpha*A*x
+ beta*y,

SYNOPSIS
SUBROUTINE CHPMV ( UPLO, N, ALPHA, AP, X, INCX, BETA, Y,
INCY )

COMPLEX      ALPHA, BETA

INTEGER      INCX, INCY, N

CHARACTER*1  UPLO

COMPLEX      AP( * ), X( * ), Y( * )

PURPOSE
CHPMV  performs the matrix-vector operation

where alpha and beta are scalars, x and y are n element vec-
tors and A is an n by n hermitian matrix, supplied in packed
form.

PARAMETERS
UPLO   - CHARACTER*1.
On entry, UPLO specifies whether the upper or lower
triangular part of the matrix A is supplied in the
packed array AP as follows:

UPLO = 'U' or 'u'   The upper triangular part of A is
supplied in AP.

UPLO = 'L' or 'l'   The lower triangular part of A is
supplied in AP.

Unchanged on exit.

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

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

AP     - COMPLEX          array of DIMENSION at least
( ( n*( n + 1 ) )/2 ).  Before entry with UPLO = 'U'
or 'u', the array AP must contain the upper triangu-
lar part of the hermitian matrix packed sequentially,
column by column, so that AP( 1 ) contains a( 1, 1 ),
AP( 2 ) and AP( 3 ) contain a( 1, 2 ) and a( 2, 2 )

respectively, and so on.  Before entry with UPLO =
'L' or 'l', the array AP must contain the lower tri-
angular part of the hermitian matrix packed sequen-
tially, column by column, so that AP( 1 ) contains a(
1, 1 ), AP( 2 ) and AP( 3 ) contain a( 2, 1 ) and a(
3, 1 ) respectively, and so on.  Note that the ima-
ginary parts of the diagonal elements need not be set
and are assumed to be zero.  Unchanged on exit.

X      - COMPLEX          array of dimension at least
( 1 + ( n - 1 )*abs( INCX ) ).  Before entry, the
incremented array X must contain the n element vector
x.  Unchanged on exit.

INCX   - INTEGER.
On entry, INCX specifies the increment for the ele-
ments of X. INCX must not be zero.  Unchanged on
exit.

BETA   - COMPLEX         .
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          array of dimension at least
( 1 + ( n - 1 )*abs( INCY ) ).  Before entry, the
incremented array Y must contain the n element vector
y. On exit, Y is overwritten by the updated vector y.

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

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.
```