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    1: *> \brief \b DAXPY
    2: *
    3: *  =========== DOCUMENTATION ===========
    4: *
    5: * Online html documentation available at 
    6: *            http://www.netlib.org/lapack/explore-html/ 
    7: *
    8: *  Definition:
    9: *  ===========
   10: *
   11: *       SUBROUTINE DAXPY(N,DA,DX,INCX,DY,INCY)
   12: * 
   13: *       .. Scalar Arguments ..
   14: *       DOUBLE PRECISION DA
   15: *       INTEGER INCX,INCY,N
   16: *       ..
   17: *       .. Array Arguments ..
   18: *       DOUBLE PRECISION DX(*),DY(*)
   19: *       ..
   20: *  
   21: *
   22: *> \par Purpose:
   23: *  =============
   24: *>
   25: *> \verbatim
   26: *>
   27: *>    DAXPY constant times a vector plus a vector.
   28: *>    uses unrolled loops for increments equal to one.
   29: *> \endverbatim
   30: *
   31: *  Authors:
   32: *  ========
   33: *
   34: *> \author Univ. of Tennessee 
   35: *> \author Univ. of California Berkeley 
   36: *> \author Univ. of Colorado Denver 
   37: *> \author NAG Ltd. 
   38: *
   39: *> \date November 2011
   40: *
   41: *> \ingroup double_blas_level1
   42: *
   43: *> \par Further Details:
   44: *  =====================
   45: *>
   46: *> \verbatim
   47: *>
   48: *>     jack dongarra, linpack, 3/11/78.
   49: *>     modified 12/3/93, array(1) declarations changed to array(*)
   50: *> \endverbatim
   51: *>
   52: *  =====================================================================
   53:       SUBROUTINE DAXPY(N,DA,DX,INCX,DY,INCY)
   54: *
   55: *  -- Reference BLAS level1 routine (version 3.4.0) --
   56: *  -- Reference BLAS is a software package provided by Univ. of Tennessee,    --
   57: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
   58: *     November 2011
   59: *
   60: *     .. Scalar Arguments ..
   61:       DOUBLE PRECISION DA
   62:       INTEGER INCX,INCY,N
   63: *     ..
   64: *     .. Array Arguments ..
   65:       DOUBLE PRECISION DX(*),DY(*)
   66: *     ..
   67: *
   68: *  =====================================================================
   69: *
   70: *     .. Local Scalars ..
   71:       INTEGER I,IX,IY,M,MP1
   72: *     ..
   73: *     .. Intrinsic Functions ..
   74:       INTRINSIC MOD
   75: *     ..
   76:       IF (N.LE.0) RETURN
   77:       IF (DA.EQ.0.0d0) RETURN
   78:       IF (INCX.EQ.1 .AND. INCY.EQ.1) THEN
   79: *
   80: *        code for both increments equal to 1
   81: *
   82: *
   83: *        clean-up loop
   84: *
   85:          M = MOD(N,4)
   86:          IF (M.NE.0) THEN
   87:             DO I = 1,M
   88:                DY(I) = DY(I) + DA*DX(I)
   89:             END DO
   90:          END IF
   91:          IF (N.LT.4) RETURN
   92:          MP1 = M + 1
   93:          DO I = MP1,N,4
   94:             DY(I) = DY(I) + DA*DX(I)
   95:             DY(I+1) = DY(I+1) + DA*DX(I+1)
   96:             DY(I+2) = DY(I+2) + DA*DX(I+2)
   97:             DY(I+3) = DY(I+3) + DA*DX(I+3)
   98:          END DO
   99:       ELSE
  100: *
  101: *        code for unequal increments or equal increments
  102: *          not equal to 1
  103: *
  104:          IX = 1
  105:          IY = 1
  106:          IF (INCX.LT.0) IX = (-N+1)*INCX + 1
  107:          IF (INCY.LT.0) IY = (-N+1)*INCY + 1
  108:          DO I = 1,N
  109:           DY(IY) = DY(IY) + DA*DX(IX)
  110:           IX = IX + INCX
  111:           IY = IY + INCY
  112:          END DO
  113:       END IF
  114:       RETURN
  115:       END