dlargv.f.html

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<pre>
      SUBROUTINE <a name="DLARGV.1"></a><a href="dlargv.f.html#DLARGV.1">DLARGV</a>( N, X, INCX, Y, INCY, C, INCC )
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  -- LAPACK auxiliary routine (version 3.1) --
</span><span class="comment">*</span><span class="comment">     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
</span><span class="comment">*</span><span class="comment">     November 2006
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     .. Scalar Arguments ..
</span>      INTEGER            INCC, INCX, INCY, N
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Array Arguments ..
</span>      DOUBLE PRECISION   C( * ), X( * ), Y( * )
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Purpose
</span><span class="comment">*</span><span class="comment">  =======
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  <a name="DLARGV.17"></a><a href="dlargv.f.html#DLARGV.1">DLARGV</a> generates a vector of real plane rotations, determined by
</span><span class="comment">*</span><span class="comment">  elements of the real vectors x and y. For i = 1,2,...,n
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     (  c(i)  s(i) ) ( x(i) ) = ( a(i) )
</span><span class="comment">*</span><span class="comment">     ( -s(i)  c(i) ) ( y(i) ) = (   0  )
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Arguments
</span><span class="comment">*</span><span class="comment">  =========
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  N       (input) INTEGER
</span><span class="comment">*</span><span class="comment">          The number of plane rotations to be generated.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  X       (input/output) DOUBLE PRECISION array,
</span><span class="comment">*</span><span class="comment">                         dimension (1+(N-1)*INCX)
</span><span class="comment">*</span><span class="comment">          On entry, the vector x.
</span><span class="comment">*</span><span class="comment">          On exit, x(i) is overwritten by a(i), for i = 1,...,n.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  INCX    (input) INTEGER
</span><span class="comment">*</span><span class="comment">          The increment between elements of X. INCX &gt; 0.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Y       (input/output) DOUBLE PRECISION array,
</span><span class="comment">*</span><span class="comment">                         dimension (1+(N-1)*INCY)
</span><span class="comment">*</span><span class="comment">          On entry, the vector y.
</span><span class="comment">*</span><span class="comment">          On exit, the sines of the plane rotations.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  INCY    (input) INTEGER
</span><span class="comment">*</span><span class="comment">          The increment between elements of Y. INCY &gt; 0.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  C       (output) DOUBLE PRECISION array, dimension (1+(N-1)*INCC)
</span><span class="comment">*</span><span class="comment">          The cosines of the plane rotations.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  INCC    (input) INTEGER
</span><span class="comment">*</span><span class="comment">          The increment between elements of C. INCC &gt; 0.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  =====================================================================
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     .. Parameters ..
</span>      DOUBLE PRECISION   ZERO, ONE
      PARAMETER          ( ZERO = 0.0D+0, ONE = 1.0D+0 )
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Local Scalars ..
</span>      INTEGER            I, IC, IX, IY
      DOUBLE PRECISION   F, G, T, TT
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Intrinsic Functions ..
</span>      INTRINSIC          ABS, SQRT
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Executable Statements ..
</span><span class="comment">*</span><span class="comment">
</span>      IX = 1
      IY = 1
      IC = 1
      DO 10 I = 1, N
         F = X( IX )
         G = Y( IY )
         IF( G.EQ.ZERO ) THEN
            C( IC ) = ONE
         ELSE IF( F.EQ.ZERO ) THEN
            C( IC ) = ZERO
            Y( IY ) = ONE
            X( IX ) = G
         ELSE IF( ABS( F ).GT.ABS( G ) ) THEN
            T = G / F
            TT = SQRT( ONE+T*T )
            C( IC ) = ONE / TT
            Y( IY ) = T*C( IC )
            X( IX ) = F*TT
         ELSE
            T = F / G
            TT = SQRT( ONE+T*T )
            Y( IY ) = ONE / TT
            C( IC ) = T*Y( IY )
            X( IX ) = G*TT
         END IF
         IC = IC + INCC
         IY = IY + INCY
         IX = IX + INCX
   10 CONTINUE
      RETURN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     End of <a name="DLARGV.97"></a><a href="dlargv.f.html#DLARGV.1">DLARGV</a>
</span><span class="comment">*</span><span class="comment">
</span>      END

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