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    1: *> \brief \b DROTM
    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 DROTM(N,DX,INCX,DY,INCY,DPARAM)
   12: * 
   13: *       .. Scalar Arguments ..
   14: *       INTEGER INCX,INCY,N
   15: *       ..
   16: *       .. Array Arguments ..
   17: *       DOUBLE PRECISION DPARAM(5),DX(*),DY(*)
   18: *       ..
   19: *  
   20: *
   21: *> \par Purpose:
   22: *  =============
   23: *>
   24: *> \verbatim
   25: *>
   26: *>    APPLY THE MODIFIED GIVENS TRANSFORMATION, H, TO THE 2 BY N MATRIX
   27: *>
   28: *>    (DX**T) , WHERE **T INDICATES TRANSPOSE. THE ELEMENTS OF DX ARE IN
   29: *>    (DY**T)
   30: *>
   31: *>    DX(LX+I*INCX), I = 0 TO N-1, WHERE LX = 1 IF INCX .GE. 0, ELSE
   32: *>    LX = (-INCX)*N, AND SIMILARLY FOR SY USING LY AND INCY.
   33: *>    WITH DPARAM(1)=DFLAG, H HAS ONE OF THE FOLLOWING FORMS..
   34: *>
   35: *>    DFLAG=-1.D0     DFLAG=0.D0        DFLAG=1.D0     DFLAG=-2.D0
   36: *>
   37: *>      (DH11  DH12)    (1.D0  DH12)    (DH11  1.D0)    (1.D0  0.D0)
   38: *>    H=(          )    (          )    (          )    (          )
   39: *>      (DH21  DH22),   (DH21  1.D0),   (-1.D0 DH22),   (0.D0  1.D0).
   40: *>    SEE DROTMG FOR A DESCRIPTION OF DATA STORAGE IN DPARAM.
   41: *> \endverbatim
   42: *
   43: *  Arguments:
   44: *  ==========
   45: *
   46: *> \param[in] N
   47: *> \verbatim
   48: *>          N is INTEGER
   49: *>         number of elements in input vector(s)
   50: *> \endverbatim
   51: *>
   52: *> \param[in,out] DX
   53: *> \verbatim
   54: *>          DX is DOUBLE PRECISION array, dimension N
   55: *>         double precision vector with N elements
   56: *> \endverbatim
   57: *>
   58: *> \param[in] INCX
   59: *> \verbatim
   60: *>          INCX is INTEGER
   61: *>         storage spacing between elements of DX
   62: *> \endverbatim
   63: *>
   64: *> \param[in,out] DY
   65: *> \verbatim
   66: *>          DY is DOUBLE PRECISION array, dimension N
   67: *>         double precision vector with N elements
   68: *> \endverbatim
   69: *>
   70: *> \param[in] INCY
   71: *> \verbatim
   72: *>          INCY is INTEGER
   73: *>         storage spacing between elements of DY
   74: *> \endverbatim
   75: *>
   76: *> \param[in,out] DPARAM
   77: *> \verbatim
   78: *>          DPARAM is DOUBLE PRECISION array, dimension 5
   79: *>     DPARAM(1)=DFLAG
   80: *>     DPARAM(2)=DH11
   81: *>     DPARAM(3)=DH21
   82: *>     DPARAM(4)=DH12
   83: *>     DPARAM(5)=DH22
   84: *> \endverbatim
   85: *
   86: *  Authors:
   87: *  ========
   88: *
   89: *> \author Univ. of Tennessee 
   90: *> \author Univ. of California Berkeley 
   91: *> \author Univ. of Colorado Denver 
   92: *> \author NAG Ltd. 
   93: *
   94: *> \date November 2011
   95: *
   96: *> \ingroup double_blas_level1
   97: *
   98: *  =====================================================================
   99:       SUBROUTINE DROTM(N,DX,INCX,DY,INCY,DPARAM)
  100: *
  101: *  -- Reference BLAS level1 routine (version 3.4.0) --
  102: *  -- Reference BLAS is a software package provided by Univ. of Tennessee,    --
  103: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
  104: *     November 2011
  105: *
  106: *     .. Scalar Arguments ..
  107:       INTEGER INCX,INCY,N
  108: *     ..
  109: *     .. Array Arguments ..
  110:       DOUBLE PRECISION DPARAM(5),DX(*),DY(*)
  111: *     ..
  112: *
  113: *  =====================================================================
  114: *
  115: *     .. Local Scalars ..
  116:       DOUBLE PRECISION DFLAG,DH11,DH12,DH21,DH22,TWO,W,Z,ZERO
  117:       INTEGER I,KX,KY,NSTEPS
  118: *     ..
  119: *     .. Data statements ..
  120:       DATA ZERO,TWO/0.D0,2.D0/
  121: *     ..
  122: *
  123:       DFLAG = DPARAM(1)
  124:       IF (N.LE.0 .OR. (DFLAG+TWO.EQ.ZERO)) RETURN
  125:       IF (INCX.EQ.INCY.AND.INCX.GT.0) THEN
  126: *
  127:          NSTEPS = N*INCX
  128:          IF (DFLAG.LT.ZERO) THEN
  129:             DH11 = DPARAM(2)
  130:             DH12 = DPARAM(4)
  131:             DH21 = DPARAM(3)
  132:             DH22 = DPARAM(5)
  133:             DO I = 1,NSTEPS,INCX
  134:                W = DX(I)
  135:                Z = DY(I)
  136:                DX(I) = W*DH11 + Z*DH12
  137:                DY(I) = W*DH21 + Z*DH22
  138:             END DO
  139:          ELSE IF (DFLAG.EQ.ZERO) THEN
  140:             DH12 = DPARAM(4)
  141:             DH21 = DPARAM(3)
  142:             DO I = 1,NSTEPS,INCX
  143:                W = DX(I)
  144:                Z = DY(I)
  145:                DX(I) = W + Z*DH12
  146:                DY(I) = W*DH21 + Z
  147:             END DO
  148:          ELSE
  149:             DH11 = DPARAM(2)
  150:             DH22 = DPARAM(5)
  151:             DO I = 1,NSTEPS,INCX
  152:                W = DX(I)
  153:                Z = DY(I)
  154:                DX(I) = W*DH11 + Z
  155:                DY(I) = -W + DH22*Z
  156:             END DO
  157:          END IF
  158:       ELSE
  159:          KX = 1
  160:          KY = 1
  161:          IF (INCX.LT.0) KX = 1 + (1-N)*INCX
  162:          IF (INCY.LT.0) KY = 1 + (1-N)*INCY
  163: *
  164:          IF (DFLAG.LT.ZERO) THEN
  165:             DH11 = DPARAM(2)
  166:             DH12 = DPARAM(4)
  167:             DH21 = DPARAM(3)
  168:             DH22 = DPARAM(5)
  169:             DO I = 1,N
  170:                W = DX(KX)
  171:                Z = DY(KY)
  172:                DX(KX) = W*DH11 + Z*DH12
  173:                DY(KY) = W*DH21 + Z*DH22
  174:                KX = KX + INCX
  175:                KY = KY + INCY
  176:             END DO
  177:          ELSE IF (DFLAG.EQ.ZERO) THEN
  178:             DH12 = DPARAM(4)
  179:             DH21 = DPARAM(3)
  180:             DO I = 1,N
  181:                W = DX(KX)
  182:                Z = DY(KY)
  183:                DX(KX) = W + Z*DH12
  184:                DY(KY) = W*DH21 + Z
  185:                KX = KX + INCX
  186:                KY = KY + INCY
  187:             END DO
  188:          ELSE
  189:              DH11 = DPARAM(2)
  190:              DH22 = DPARAM(5)
  191:              DO I = 1,N
  192:                 W = DX(KX)
  193:                 Z = DY(KY)
  194:                 DX(KX) = W*DH11 + Z
  195:                 DY(KY) = -W + DH22*Z
  196:                 KX = KX + INCX
  197:                 KY = KY + INCY
  198:             END DO
  199:          END IF
  200:       END IF
  201:       RETURN
  202:       END