dlassq.f.html

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      SUBROUTINE <a name="DLASSQ.1"></a><a href="dlassq.f.html#DLASSQ.1">DLASSQ</a>( N, X, INCX, SCALE, SUMSQ )
<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            INCX, N
      DOUBLE PRECISION   SCALE, SUMSQ
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Array Arguments ..
</span>      DOUBLE PRECISION   X( * )
<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="DLASSQ.18"></a><a href="dlassq.f.html#DLASSQ.1">DLASSQ</a>  returns the values  scl  and  smsq  such that
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     ( scl**2 )*smsq = x( 1 )**2 +...+ x( n )**2 + ( scale**2 )*sumsq,
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  where  x( i ) = X( 1 + ( i - 1 )*INCX ). The value of  sumsq  is
</span><span class="comment">*</span><span class="comment">  assumed to be non-negative and  scl  returns the value
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     scl = max( scale, abs( x( i ) ) ).
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  scale and sumsq must be supplied in SCALE and SUMSQ and
</span><span class="comment">*</span><span class="comment">  scl and smsq are overwritten on SCALE and SUMSQ respectively.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  The routine makes only one pass through the vector x.
</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 elements to be used from the vector X.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  X       (input) DOUBLE PRECISION array, dimension (N)
</span><span class="comment">*</span><span class="comment">          The vector for which a scaled sum of squares is computed.
</span><span class="comment">*</span><span class="comment">             x( i )  = X( 1 + ( i - 1 )*INCX ), 1 &lt;= i &lt;= 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 successive values of the vector X.
</span><span class="comment">*</span><span class="comment">          INCX &gt; 0.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  SCALE   (input/output) DOUBLE PRECISION
</span><span class="comment">*</span><span class="comment">          On entry, the value  scale  in the equation above.
</span><span class="comment">*</span><span class="comment">          On exit, SCALE is overwritten with  scl , the scaling factor
</span><span class="comment">*</span><span class="comment">          for the sum of squares.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  SUMSQ   (input/output) DOUBLE PRECISION
</span><span class="comment">*</span><span class="comment">          On entry, the value  sumsq  in the equation above.
</span><span class="comment">*</span><span class="comment">          On exit, SUMSQ is overwritten with  smsq , the basic sum of
</span><span class="comment">*</span><span class="comment">          squares from which  scl  has been factored out.
</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
      PARAMETER          ( ZERO = 0.0D+0 )
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Local Scalars ..
</span>      INTEGER            IX
      DOUBLE PRECISION   ABSXI
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Intrinsic Functions ..
</span>      INTRINSIC          ABS
<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>      IF( N.GT.0 ) THEN
         DO 10 IX = 1, 1 + ( N-1 )*INCX, INCX
            IF( X( IX ).NE.ZERO ) THEN
               ABSXI = ABS( X( IX ) )
               IF( SCALE.LT.ABSXI ) THEN
                  SUMSQ = 1 + SUMSQ*( SCALE / ABSXI )**2
                  SCALE = ABSXI
               ELSE
                  SUMSQ = SUMSQ + ( ABSXI / SCALE )**2
               END IF
            END IF
   10    CONTINUE
      END IF
      RETURN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     End of <a name="DLASSQ.86"></a><a href="dlassq.f.html#DLASSQ.1">DLASSQ</a>
</span><span class="comment">*</span><span class="comment">
</span>      END

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