OpenBLAS/lapack-netlib/BLAS/SRC/sspr.f

*> \brief \b SSPR
*
*  =========== DOCUMENTATION ===========
*
* Online html documentation available at 
*            http://www.netlib.org/lapack/explore-html/ 
*
*  Definition:
*  ===========
*
*       SUBROUTINE SSPR(UPLO,N,ALPHA,X,INCX,AP)
* 
*       .. Scalar Arguments ..
*       REAL ALPHA
*       INTEGER INCX,N
*       CHARACTER UPLO
*       ..
*       .. Array Arguments ..
*       REAL AP(*),X(*)
*       ..
*  
*
*> \par Purpose:
*  =============
*>
*> \verbatim
*>
*> SSPR    performs the symmetric rank 1 operation
*>
*>    A := alpha*x*x**T + A,
*>
*> where alpha is a real 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.
*> \endverbatim
*>
*> \param[in] N
*> \verbatim
*>          N is INTEGER
*>           On entry, N specifies the order of the matrix A.
*>           N must be at least zero.
*> \endverbatim
*>
*> \param[in] ALPHA
*> \verbatim
*>          ALPHA is REAL
*>           On entry, ALPHA specifies the scalar alpha.
*> \endverbatim
*>
*> \param[in] X
*> \verbatim
*>          X is REAL array of dimension at least
*>           ( 1 + ( n - 1 )*abs( INCX ) ).
*>           Before entry, the incremented array X must contain the n
*>           element vector x.
*> \endverbatim
*>
*> \param[in] INCX
*> \verbatim
*>          INCX is INTEGER
*>           On entry, INCX specifies the increment for the elements of
*>           X. INCX must not be zero.
*> \endverbatim
*>
*> \param[in,out] AP
*> \verbatim
*>          AP is REAL 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 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.
*> \endverbatim
*
*  Authors:
*  ========
*
*> \author Univ. of Tennessee 
*> \author Univ. of California Berkeley 
*> \author Univ. of Colorado Denver 
*> \author NAG Ltd. 
*
*> \date November 2011
*
*> \ingroup single_blas_level2
*
*> \par Further Details:
*  =====================
*>
*> \verbatim
*>
*>  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.
*> \endverbatim
*>
*  =====================================================================
      SUBROUTINE SSPR(UPLO,N,ALPHA,X,INCX,AP)
*
*  -- Reference BLAS level2 routine (version 3.4.0) --
*  -- Reference BLAS is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*     November 2011
*
*     .. Scalar Arguments ..
      REAL ALPHA
      INTEGER INCX,N
      CHARACTER UPLO
*     ..
*     .. Array Arguments ..
      REAL AP(*),X(*)
*     ..
*
*  =====================================================================
*
*     .. Parameters ..
      REAL ZERO
      PARAMETER (ZERO=0.0E+0)
*     ..
*     .. Local Scalars ..
      REAL TEMP
      INTEGER I,INFO,IX,J,JX,K,KK,KX
*     ..
*     .. External Functions ..
      LOGICAL LSAME
      EXTERNAL LSAME
*     ..
*     .. External Subroutines ..
      EXTERNAL XERBLA
*     ..
*
*     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('SSPR  ',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
                          AP(K) = AP(K) + X(I)*TEMP
                          K = K + 1
   10                 CONTINUE
                  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 - 1
                          AP(K) = AP(K) + X(IX)*TEMP
                          IX = IX + INCX
   30                 CONTINUE
                  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)
                      K = KK
                      DO 50 I = J,N
                          AP(K) = AP(K) + X(I)*TEMP
                          K = K + 1
   50                 CONTINUE
                  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)
                      IX = JX
                      DO 70 K = KK,KK + N - J
                          AP(K) = AP(K) + X(IX)*TEMP
                          IX = IX + INCX
   70                 CONTINUE
                  END IF
                  JX = JX + INCX
                  KK = KK + N - J + 1
   80         CONTINUE
          END IF
      END IF
*
      RETURN
*
*     End of SSPR  .
*
      END