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261 lines
6.9 KiB
261 lines
6.9 KiB
2 years ago
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*> \brief \b SSYR
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*
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* =========== DOCUMENTATION ===========
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*
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* Online html documentation available at
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* http://www.netlib.org/lapack/explore-html/
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*
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* Definition:
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* ===========
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*
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* SUBROUTINE SSYR(UPLO,N,ALPHA,X,INCX,A,LDA)
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*
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* .. Scalar Arguments ..
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* REAL ALPHA
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* INTEGER INCX,LDA,N
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* CHARACTER UPLO
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* ..
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* .. Array Arguments ..
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* REAL A(LDA,*),X(*)
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* ..
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*
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*
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*> \par Purpose:
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* =============
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*>
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*> \verbatim
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*>
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*> SSYR performs the symmetric rank 1 operation
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*>
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*> A := alpha*x*x**T + A,
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*>
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*> where alpha is a real scalar, x is an n element vector and A is an
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*> n by n symmetric matrix.
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*> \endverbatim
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*
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* Arguments:
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* ==========
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*
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*> \param[in] UPLO
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*> \verbatim
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*> UPLO is CHARACTER*1
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*> On entry, UPLO specifies whether the upper or lower
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*> triangular part of the array A is to be referenced as
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*> follows:
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*>
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*> UPLO = 'U' or 'u' Only the upper triangular part of A
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*> is to be referenced.
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*>
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*> UPLO = 'L' or 'l' Only the lower triangular part of A
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*> is to be referenced.
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*> \endverbatim
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*>
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*> \param[in] N
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*> \verbatim
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*> N is INTEGER
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*> On entry, N specifies the order of the matrix A.
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*> N must be at least zero.
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*> \endverbatim
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*>
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*> \param[in] ALPHA
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*> \verbatim
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*> ALPHA is REAL
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*> On entry, ALPHA specifies the scalar alpha.
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*> \endverbatim
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*>
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*> \param[in] X
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*> \verbatim
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*> X is REAL array, dimension at least
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*> ( 1 + ( n - 1 )*abs( INCX ) ).
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*> Before entry, the incremented array X must contain the n
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*> element vector x.
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*> \endverbatim
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*>
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*> \param[in] INCX
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*> \verbatim
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*> INCX is INTEGER
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*> On entry, INCX specifies the increment for the elements of
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*> X. INCX must not be zero.
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*> \endverbatim
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*>
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*> \param[in,out] A
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*> \verbatim
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*> A is REAL array, dimension ( LDA, N )
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*> Before entry with UPLO = 'U' or 'u', the leading n by n
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*> upper triangular part of the array A must contain the upper
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*> triangular part of the symmetric matrix and the strictly
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*> lower triangular part of A is not referenced. On exit, the
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*> upper triangular part of the array A is overwritten by the
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*> upper triangular part of the updated matrix.
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*> Before entry with UPLO = 'L' or 'l', the leading n by n
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*> lower triangular part of the array A must contain the lower
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*> triangular part of the symmetric matrix and the strictly
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*> upper triangular part of A is not referenced. On exit, the
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*> lower triangular part of the array A is overwritten by the
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*> lower triangular part of the updated matrix.
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*> \endverbatim
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*>
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*> \param[in] LDA
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*> \verbatim
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*> LDA is INTEGER
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*> On entry, LDA specifies the first dimension of A as declared
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*> in the calling (sub) program. LDA must be at least
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*> max( 1, n ).
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*> \endverbatim
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*
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* Authors:
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* ========
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*
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*> \author Univ. of Tennessee
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*> \author Univ. of California Berkeley
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*> \author Univ. of Colorado Denver
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*> \author NAG Ltd.
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*
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*> \ingroup single_blas_level2
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*
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*> \par Further Details:
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* =====================
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*>
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*> \verbatim
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*>
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*> Level 2 Blas routine.
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*>
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*> -- Written on 22-October-1986.
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*> Jack Dongarra, Argonne National Lab.
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*> Jeremy Du Croz, Nag Central Office.
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*> Sven Hammarling, Nag Central Office.
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*> Richard Hanson, Sandia National Labs.
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*> \endverbatim
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*>
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* =====================================================================
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SUBROUTINE SSYR(UPLO,N,ALPHA,X,INCX,A,LDA)
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*
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* -- Reference BLAS level2 routine --
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* -- Reference BLAS is a software package provided by Univ. of Tennessee, --
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* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
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*
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* .. Scalar Arguments ..
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REAL ALPHA
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INTEGER INCX,LDA,N
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CHARACTER UPLO
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* ..
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* .. Array Arguments ..
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REAL A(LDA,*),X(*)
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* ..
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*
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* =====================================================================
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*
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* .. Parameters ..
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REAL ZERO
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PARAMETER (ZERO=0.0E+0)
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* ..
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* .. Local Scalars ..
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REAL TEMP
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INTEGER I,INFO,IX,J,JX,KX
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* ..
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* .. External Functions ..
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LOGICAL LSAME
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EXTERNAL LSAME
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* ..
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* .. External Subroutines ..
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EXTERNAL XERBLA
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC MAX
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* ..
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*
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* Test the input parameters.
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*
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INFO = 0
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IF (.NOT.LSAME(UPLO,'U') .AND. .NOT.LSAME(UPLO,'L')) THEN
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INFO = 1
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ELSE IF (N.LT.0) THEN
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INFO = 2
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ELSE IF (INCX.EQ.0) THEN
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INFO = 5
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ELSE IF (LDA.LT.MAX(1,N)) THEN
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INFO = 7
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END IF
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IF (INFO.NE.0) THEN
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CALL XERBLA('SSYR ',INFO)
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RETURN
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END IF
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*
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* Quick return if possible.
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*
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IF ((N.EQ.0) .OR. (ALPHA.EQ.ZERO)) RETURN
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*
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* Set the start point in X if the increment is not unity.
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*
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IF (INCX.LE.0) THEN
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KX = 1 - (N-1)*INCX
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ELSE IF (INCX.NE.1) THEN
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KX = 1
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END IF
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*
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* Start the operations. In this version the elements of A are
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* accessed sequentially with one pass through the triangular part
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* of A.
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*
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IF (LSAME(UPLO,'U')) THEN
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*
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* Form A when A is stored in upper triangle.
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*
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IF (INCX.EQ.1) THEN
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DO 20 J = 1,N
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IF (X(J).NE.ZERO) THEN
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TEMP = ALPHA*X(J)
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DO 10 I = 1,J
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A(I,J) = A(I,J) + X(I)*TEMP
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10 CONTINUE
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END IF
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20 CONTINUE
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ELSE
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JX = KX
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DO 40 J = 1,N
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IF (X(JX).NE.ZERO) THEN
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TEMP = ALPHA*X(JX)
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IX = KX
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DO 30 I = 1,J
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A(I,J) = A(I,J) + X(IX)*TEMP
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IX = IX + INCX
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30 CONTINUE
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END IF
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JX = JX + INCX
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40 CONTINUE
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END IF
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ELSE
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*
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* Form A when A is stored in lower triangle.
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*
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IF (INCX.EQ.1) THEN
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DO 60 J = 1,N
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IF (X(J).NE.ZERO) THEN
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TEMP = ALPHA*X(J)
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DO 50 I = J,N
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A(I,J) = A(I,J) + X(I)*TEMP
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50 CONTINUE
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END IF
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60 CONTINUE
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ELSE
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JX = KX
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DO 80 J = 1,N
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IF (X(JX).NE.ZERO) THEN
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TEMP = ALPHA*X(JX)
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IX = JX
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DO 70 I = J,N
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A(I,J) = A(I,J) + X(IX)*TEMP
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IX = IX + INCX
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70 CONTINUE
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END IF
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JX = JX + INCX
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80 CONTINUE
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END IF
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END IF
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*
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RETURN
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*
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* End of SSYR
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*
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END
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