SUBROUTINE SSYR2 (UPLO, N, ALPHA, X, INCX, Y, INCY, A, LDA)
C     .. Scalar Arguments ..
      REAL               ALPHA
      INTEGER            INCX, INCY, LDA, N
      CHARACTER*1        UPLO
C     .. Array Arguments ..
      REAL               A( LDA, * ), X( * ), Y( * )
C     .. Parameters ..
      REAL               ZERO
      PARAMETER        ( ZERO = 0.0E+0 )
C     .. Local Scalars ..
      REAL               TEMP1, TEMP2
      INTEGER            I, INFO, IX, IY, J, JX, JY, KX, KY
C     .. External Functions ..
      LOGICAL            LSAME
      EXTERNAL           LSAME
C     .. External Subroutines ..
      EXTERNAL           XERBLA
C     .. Intrinsic Functions ..
      INTRINSIC          MAX
C***FIRST EXECUTABLE STATEMENT  SSYR2
C
C     Test the input parameters.
C
      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
      ELSE IF( INCY.EQ.0 )THEN
         INFO = 7
      ELSE IF( LDA.LT.MAX( 1, N ) )THEN
         INFO = 9
      END IF
      IF( INFO.NE.0 )THEN
         CALL XERBLA( 'SSYR2 ', INFO )
         RETURN
      END IF
C
C     Quick return if possible.
C
      IF( ( N.EQ.0 ).OR.( ALPHA.EQ.ZERO ) )
     $   RETURN
C
C     Set up the start points in X and Y if the increments are not both
C     unity.
C
      IF( ( INCX.NE.1 ).OR.( INCY.NE.1 ) )THEN
         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
         JX = KX
         JY = KY
      END IF
C
C     Start the operations. In this version the elements of A are
C     accessed sequentially with one pass through the triangular part
C     of A.
C
      IF( LSAME( UPLO, 'U' ) )THEN
C
C        Form  A  when A is stored in the upper triangle.
C
         IF( ( INCX.EQ.1 ).AND.( INCY.EQ.1 ) )THEN
            DO 20, J = 1, N
               IF( ( X( J ).NE.ZERO ).OR.( Y( J ).NE.ZERO ) )THEN
                  TEMP1 = ALPHA*Y( J )
                  TEMP2 = ALPHA*X( J )
                  DO 10, I = 1, J
                     A( I, J ) = A( I, J ) + X( I )*TEMP1 + Y( I )*TEMP2
   10             CONTINUE
               END IF
   20       CONTINUE
         ELSE
            DO 40, J = 1, N
               IF( ( X( JX ).NE.ZERO ).OR.( Y( JY ).NE.ZERO ) )THEN
                  TEMP1 = ALPHA*Y( JY )
                  TEMP2 = ALPHA*X( JX )
                  IX    = KX
                  IY    = KY
                  DO 30, I = 1, J
                     A( I, J ) = A( I, J ) + X( IX )*TEMP1
     $                                     + Y( IY )*TEMP2
                     IX        = IX        + INCX
                     IY        = IY        + INCY
   30             CONTINUE
               END IF
               JX = JX + INCX
               JY = JY + INCY
   40       CONTINUE
         END IF
      ELSE
C
C        Form  A  when A is stored in the lower triangle.
C
         IF( ( INCX.EQ.1 ).AND.( INCY.EQ.1 ) )THEN
            DO 60, J = 1, N
               IF( ( X( J ).NE.ZERO ).OR.( Y( J ).NE.ZERO ) )THEN
                  TEMP1 = ALPHA*Y( J )
                  TEMP2 = ALPHA*X( J )
                  DO 50, I = J, N
                     A( I, J ) = A( I, J ) + X( I )*TEMP1 + Y( I )*TEMP2
   50             CONTINUE
               END IF
   60       CONTINUE
         ELSE
            DO 80, J = 1, N
               IF( ( X( JX ).NE.ZERO ).OR.( Y( JY ).NE.ZERO ) )THEN
                  TEMP1 = ALPHA*Y( JY )
                  TEMP2 = ALPHA*X( JX )
                  IX    = JX
                  IY    = JY
                  DO 70, I = J, N
                     A( I, J ) = A( I, J ) + X( IX )*TEMP1
     $                                     + Y( IY )*TEMP2
                     IX        = IX        + INCX
                     IY        = IY        + INCY
   70             CONTINUE
               END IF
               JX = JX + INCX
               JY = JY + INCY
   80       CONTINUE
         END IF
      END IF
C
      RETURN
C
C     End of SSYR2 .
C
      END