Man Linux: Main Page and Category List

## NAME

```       CHPR2 - perform the hermitian rank 2 operation   A := alpha*x*conjg( y’
) + conjg( alpha )*y*conjg( x’ ) + A,

```

## SYNOPSIS

```       SUBROUTINE CHPR2 ( UPLO, N, ALPHA, X, INCX, Y, INCY, AP )

COMPLEX      ALPHA

INTEGER      INCX, INCY, N

CHARACTER*1  UPLO

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

```

## PURPOSE

```       CHPR2  performs the hermitian rank 2 operation

where alpha is a scalar, x and y are n element vectors 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.

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 elements of X.
INCX must not be zero.  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.  Unchanged on exit.

INCY   - INTEGER.
On entry, INCY specifies the increment for the  elements  of  Y.
INCY must not be zero.  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  triangular  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. On exit, the array AP
is overwritten by the  upper  triangular  part  of  the  updated
matrix.   Before entry with UPLO = ’L’ or ’l’, the array AP must
contain the lower triangular 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(  2,  1  )  and  a(  3,  1  )
respectively, and so on. On exit, the array AP is overwritten by
the lower triangular part of the updated matrix.  Note that  the
imaginary  parts  of the diagonal elements need not be set, they
are assumed to be zero, and on exit they are set to zero.

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.
```