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lapack/SRC/cspr.f
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Julie e18d437924 Making LAPACK's code eternal... no more version and date in source files. 
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2021-03-25 10:16:58 -07:00

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*> \brief \b CSPR performs the symmetrical rank-1 update of a complex symmetric packed matrix.
*
* =========== DOCUMENTATION ===========
*
* Online html documentation available at
* http://www.netlib.org/lapack/explore-html/
*
*> \htmlonly
*> Download CSPR + dependencies
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/cspr.f">
*> [TGZ]</a>
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/cspr.f">
*> [ZIP]</a>
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/cspr.f">
*> [TXT]</a>
*> \endhtmlonly
*
* Definition:
* ===========
*
* SUBROUTINE CSPR( UPLO, N, ALPHA, X, INCX, AP )
*
* .. Scalar Arguments ..
* CHARACTER UPLO
* INTEGER INCX, N
* COMPLEX ALPHA
* ..
* .. Array Arguments ..
* COMPLEX AP( * ), X( * )
* ..
*
*
*> \par Purpose:
* =============
*>
*> \verbatim
*>
*> CSPR performs the symmetric rank 1 operation
*>
*> A := alpha*x*x**H + A,
*>
*> where alpha is a complex scalar, x is an n element vector and A is an
*> n by n symmetric matrix, supplied in packed form.
*> \endverbatim
*
* Arguments:
* ==========
*
*> \param[in] UPLO
*> \verbatim
*> UPLO is 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.
*> \endverbatim
*>
*> \param[in] N
*> \verbatim
*> N is INTEGER
*> On entry, N specifies the order of the matrix A.
*> N must be at least zero.
*> Unchanged on exit.
*> \endverbatim
*>
*> \param[in] ALPHA
*> \verbatim
*> ALPHA is COMPLEX
*> On entry, ALPHA specifies the scalar alpha.
*> Unchanged on exit.
*> \endverbatim
*>
*> \param[in] X
*> \verbatim
*> X is COMPLEX 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.
*> \endverbatim
*>
*> \param[in] INCX
*> \verbatim
*> INCX is INTEGER
*> On entry, INCX specifies the increment for the elements of
*> X. INCX must not be zero.
*> Unchanged on exit.
*> \endverbatim
*>
*> \param[in,out] AP
*> \verbatim
*> AP is COMPLEX 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. 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 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. 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.
*> \endverbatim
*
* Authors:
* ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \ingroup complexOTHERauxiliary
*
* =====================================================================
SUBROUTINE CSPR( UPLO, N, ALPHA, X, INCX, AP )
*
* -- LAPACK auxiliary routine --
* -- LAPACK is a software package provided by Univ. of Tennessee, --
* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*
* .. Scalar Arguments ..
CHARACTER UPLO
INTEGER INCX, N
COMPLEX ALPHA
* ..
* .. Array Arguments ..
COMPLEX AP( * ), X( * )
* ..
*
* =====================================================================
*
* .. Parameters ..
COMPLEX ZERO
PARAMETER ( ZERO = ( 0.0E+0, 0.0E+0 ) )
* ..
* .. Local Scalars ..
INTEGER I, INFO, IX, J, JX, K, KK, KX
COMPLEX TEMP
* ..
* .. 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 = 5
END IF
IF( INFO.NE.0 ) THEN
CALL XERBLA( 'CSPR ', INFO )
RETURN
END IF
*
* Quick return if possible.
*
IF( ( N.EQ.0 ) .OR. ( ALPHA.EQ.ZERO ) )
$ RETURN
*
* Set the start point in X if the increment is not unity.
*
IF( INCX.LE.0 ) THEN
KX = 1 - ( N-1 )*INCX
ELSE IF( INCX.NE.1 ) THEN
KX = 1
END IF
*
* Start the operations. In this version the elements of the array AP
* are accessed sequentially with one pass through AP.
*
KK = 1
IF( LSAME( UPLO, 'U' ) ) THEN
*
* Form A when upper triangle is stored in AP.
*
IF( INCX.EQ.1 ) THEN
DO 20 J = 1, N
IF( X( J ).NE.ZERO ) THEN
TEMP = ALPHA*X( J )
K = KK
DO 10 I = 1, J - 1
AP( K ) = AP( K ) + X( I )*TEMP
K = K + 1
10 CONTINUE
AP( KK+J-1 ) = AP( KK+J-1 ) + X( J )*TEMP
ELSE
AP( KK+J-1 ) = AP( KK+J-1 )
END IF
KK = KK + J
20 CONTINUE
ELSE
JX = KX
DO 40 J = 1, N
IF( X( JX ).NE.ZERO ) THEN
TEMP = ALPHA*X( JX )
IX = KX
DO 30 K = KK, KK + J - 2
AP( K ) = AP( K ) + X( IX )*TEMP
IX = IX + INCX
30 CONTINUE
AP( KK+J-1 ) = AP( KK+J-1 ) + X( JX )*TEMP
ELSE
AP( KK+J-1 ) = AP( KK+J-1 )
END IF
JX = JX + INCX
KK = KK + J
40 CONTINUE
END IF
ELSE
*
* Form A when lower triangle is stored in AP.
*
IF( INCX.EQ.1 ) THEN
DO 60 J = 1, N
IF( X( J ).NE.ZERO ) THEN
TEMP = ALPHA*X( J )
AP( KK ) = AP( KK ) + TEMP*X( J )
K = KK + 1
DO 50 I = J + 1, N
AP( K ) = AP( K ) + X( I )*TEMP
K = K + 1
50 CONTINUE
ELSE
AP( KK ) = AP( KK )
END IF
KK = KK + N - J + 1
60 CONTINUE
ELSE
JX = KX
DO 80 J = 1, N
IF( X( JX ).NE.ZERO ) THEN
TEMP = ALPHA*X( JX )
AP( KK ) = AP( KK ) + TEMP*X( JX )
IX = JX
DO 70 K = KK + 1, KK + N - J
IX = IX + INCX
AP( K ) = AP( K ) + X( IX )*TEMP
70 CONTINUE
ELSE
AP( KK ) = AP( KK )
END IF
JX = JX + INCX
KK = KK + N - J + 1
80 CONTINUE
END IF
END IF
*
RETURN
*
* End of CSPR
*
END
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