Return to dlargv.f CVS log

Up to [local] / rpl / lapack / lapack

Commit initial.

    1:       SUBROUTINE DLARGV( N, X, INCX, Y, INCY, C, INCC )
    2: *
    3: *  -- LAPACK auxiliary routine (version 3.2) --
    4: *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
    5: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
    6: *     November 2006
    7: *
    8: *     .. Scalar Arguments ..
    9:       INTEGER            INCC, INCX, INCY, N
   10: *     ..
   11: *     .. Array Arguments ..
   12:       DOUBLE PRECISION   C( * ), X( * ), Y( * )
   13: *     ..
   14: *
   15: *  Purpose
   16: *  =======
   17: *
   18: *  DLARGV generates a vector of real plane rotations, determined by
   19: *  elements of the real vectors x and y. For i = 1,2,...,n
   20: *
   21: *     (  c(i)  s(i) ) ( x(i) ) = ( a(i) )
   22: *     ( -s(i)  c(i) ) ( y(i) ) = (   0  )
   23: *
   24: *  Arguments
   25: *  =========
   26: *
   27: *  N       (input) INTEGER
   28: *          The number of plane rotations to be generated.
   29: *
   30: *  X       (input/output) DOUBLE PRECISION array,
   31: *                         dimension (1+(N-1)*INCX)
   32: *          On entry, the vector x.
   33: *          On exit, x(i) is overwritten by a(i), for i = 1,...,n.
   34: *
   35: *  INCX    (input) INTEGER
   36: *          The increment between elements of X. INCX > 0.
   37: *
   38: *  Y       (input/output) DOUBLE PRECISION array,
   39: *                         dimension (1+(N-1)*INCY)
   40: *          On entry, the vector y.
   41: *          On exit, the sines of the plane rotations.
   42: *
   43: *  INCY    (input) INTEGER
   44: *          The increment between elements of Y. INCY > 0.
   45: *
   46: *  C       (output) DOUBLE PRECISION array, dimension (1+(N-1)*INCC)
   47: *          The cosines of the plane rotations.
   48: *
   49: *  INCC    (input) INTEGER
   50: *          The increment between elements of C. INCC > 0.
   51: *
   52: *  =====================================================================
   53: *
   54: *     .. Parameters ..
   55:       DOUBLE PRECISION   ZERO, ONE
   56:       PARAMETER          ( ZERO = 0.0D+0, ONE = 1.0D+0 )
   57: *     ..
   58: *     .. Local Scalars ..
   59:       INTEGER            I, IC, IX, IY
   60:       DOUBLE PRECISION   F, G, T, TT
   61: *     ..
   62: *     .. Intrinsic Functions ..
   63:       INTRINSIC          ABS, SQRT
   64: *     ..
   65: *     .. Executable Statements ..
   66: *
   67:       IX = 1
   68:       IY = 1
   69:       IC = 1
   70:       DO 10 I = 1, N
   71:          F = X( IX )
   72:          G = Y( IY )
   73:          IF( G.EQ.ZERO ) THEN
   74:             C( IC ) = ONE
   75:          ELSE IF( F.EQ.ZERO ) THEN
   76:             C( IC ) = ZERO
   77:             Y( IY ) = ONE
   78:             X( IX ) = G
   79:          ELSE IF( ABS( F ).GT.ABS( G ) ) THEN
   80:             T = G / F
   81:             TT = SQRT( ONE+T*T )
   82:             C( IC ) = ONE / TT
   83:             Y( IY ) = T*C( IC )
   84:             X( IX ) = F*TT
   85:          ELSE
   86:             T = F / G
   87:             TT = SQRT( ONE+T*T )
   88:             Y( IY ) = ONE / TT
   89:             C( IC ) = T*Y( IY )
   90:             X( IX ) = G*TT
   91:          END IF
   92:          IC = IC + INCC
   93:          IY = IY + INCY
   94:          IX = IX + INCX
   95:    10 CONTINUE
   96:       RETURN
   97: *
   98: *     End of DLARGV
   99: *
  100:       END