SUBROUTINE ZSPMV( UPLO, N, ALPHA, AP, X, INCX, BETA, Y, INCY )
*
* -- LAPACK auxiliary routine (version 3.1) --
* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
* November 2006
*
* .. Scalar Arguments ..
CHARACTER UPLO
INTEGER INCX, INCY, N
COMPLEX*16 ALPHA, BETA
* ..
* .. Array Arguments ..
COMPLEX*16 AP( * ), X( * ), Y( * )
* ..
*
* Purpose
* =======
*
* ZSPMV performs the matrix-vector 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 matrix, supplied in packed form.
*
* Arguments
* ==========
*
* UPLO (input) 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 (input) INTEGER
* On entry, N specifies the order of the matrix A.
* N must be at least zero.
* Unchanged on exit.
*
* ALPHA (input) COMPLEX*16
* On entry, ALPHA specifies the scalar alpha.
* Unchanged on exit.
*
* AP (input) COMPLEX*16 array, 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 symmetric 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 triangular part of the symmetric 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.
* Unchanged on exit.
*
* X (input) COMPLEX*16 array, 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 (input) INTEGER
* On entry, INCX specifies the increment for the elements of
* X. INCX must not be zero.
* Unchanged on exit.
*
* BETA (input) 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 (input/output) COMPLEX*16 array, 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 (input) INTEGER
* On entry, INCY specifies the increment for the elements of
* Y. INCY must not be zero.
* Unchanged on exit.
*
* =====================================================================
*
* .. Parameters ..
COMPLEX*16 ONE
PARAMETER ( ONE = ( 1.0D+0, 0.0D+0 ) )
COMPLEX*16 ZERO
PARAMETER ( ZERO = ( 0.0D+0, 0.0D+0 ) )
* ..
* .. Local Scalars ..
INTEGER I, INFO, IX, IY, J, JX, JY, K, KK, KX, KY
COMPLEX*16 TEMP1, TEMP2
* ..
* .. External Functions ..
LOGICAL LSAME
EXTERNAL LSAME
* ..
* .. External Subroutines ..
EXTERNAL XERBLA
* ..
* .. Executable Statements ..
*
* Test the input parameters.
*
INFO = 0
IF( .NOT.LSAME( UPLO, 'U' ) .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
INFO = 1
ELSE IF( N.LT.0 ) THEN
INFO = 2
ELSE IF( INCX.EQ.0 ) THEN
INFO = 6
ELSE IF( INCY.EQ.0 ) THEN
INFO = 9
END IF
IF( INFO.NE.0 ) THEN
CALL XERBLA( 'ZSPMV ', INFO )
RETURN
END IF
*
* Quick return if possible.
*
IF( ( N.EQ.0 ) .OR. ( ( ALPHA.EQ.ZERO ) .AND. ( BETA.EQ.ONE ) ) )
$ RETURN
*
* Set up the start points in X and Y.
*
IF( INCX.GT.0 ) THEN
KX = 1
ELSE
KX = 1 - ( N-1 )*INCX
END IF
IF( INCY.GT.0 ) THEN
KY = 1
ELSE
KY = 1 - ( N-1 )*INCY
END IF
*
* Start the operations. In this version the elements of the array AP
* are accessed sequentially with one pass through AP.
*
* First form y := beta*y.
*
IF( BETA.NE.ONE ) THEN
IF( INCY.EQ.1 ) THEN
IF( BETA.EQ.ZERO ) THEN
DO 10 I = 1, N
Y( I ) = ZERO
10 CONTINUE
ELSE
DO 20 I = 1, N
Y( I ) = BETA*Y( I )
20 CONTINUE
END IF
ELSE
IY = KY
IF( BETA.EQ.ZERO ) THEN
DO 30 I = 1, N
Y( IY ) = ZERO
IY = IY + INCY
30 CONTINUE
ELSE
DO 40 I = 1, N
Y( IY ) = BETA*Y( IY )
IY = IY + INCY
40 CONTINUE
END IF
END IF
END IF
IF( ALPHA.EQ.ZERO )
$ RETURN
KK = 1
IF( LSAME( UPLO, 'U' ) ) THEN
*
* Form y when AP contains the upper triangle.
*
IF( ( INCX.EQ.1 ) .AND. ( INCY.EQ.1 ) ) THEN
DO 60 J = 1, N
TEMP1 = ALPHA*X( J )
TEMP2 = ZERO
K = KK
DO 50 I = 1, J - 1
Y( I ) = Y( I ) + TEMP1*AP( K )
TEMP2 = TEMP2 + AP( K )*X( I )
K = K + 1
50 CONTINUE
Y( J ) = Y( J ) + TEMP1*AP( KK+J-1 ) + ALPHA*TEMP2
KK = KK + J
60 CONTINUE
ELSE
JX = KX
JY = KY
DO 80 J = 1, N
TEMP1 = ALPHA*X( JX )
TEMP2 = ZERO
IX = KX
IY = KY
DO 70 K = KK, KK + J - 2
Y( IY ) = Y( IY ) + TEMP1*AP( K )
TEMP2 = TEMP2 + AP( K )*X( IX )
IX = IX + INCX
IY = IY + INCY
70 CONTINUE
Y( JY ) = Y( JY ) + TEMP1*AP( KK+J-1 ) + ALPHA*TEMP2
JX = JX + INCX
JY = JY + INCY
KK = KK + J
80 CONTINUE
END IF
ELSE
*
* Form y when AP contains the lower triangle.
*
IF( ( INCX.EQ.1 ) .AND. ( INCY.EQ.1 ) ) THEN
DO 100 J = 1, N
TEMP1 = ALPHA*X( J )
TEMP2 = ZERO
Y( J ) = Y( J ) + TEMP1*AP( KK )
K = KK + 1
DO 90 I = J + 1, N
Y( I ) = Y( I ) + TEMP1*AP( K )
TEMP2 = TEMP2 + AP( K )*X( I )
K = K + 1
90 CONTINUE
Y( J ) = Y( J ) + ALPHA*TEMP2
KK = KK + ( N-J+1 )
100 CONTINUE
ELSE
JX = KX
JY = KY
DO 120 J = 1, N
TEMP1 = ALPHA*X( JX )
TEMP2 = ZERO
Y( JY ) = Y( JY ) + TEMP1*AP( KK )
IX = JX
IY = JY
DO 110 K = KK + 1, KK + N - J
IX = IX + INCX
IY = IY + INCY
Y( IY ) = Y( IY ) + TEMP1*AP( K )
TEMP2 = TEMP2 + AP( K )*X( IX )
110 CONTINUE
Y( JY ) = Y( JY ) + ALPHA*TEMP2
JX = JX + INCX
JY = JY + INCY
KK = KK + ( N-J+1 )
120 CONTINUE
END IF
END IF
*
RETURN
*
* End of ZSPMV
*
END