dnrm2()

double precision function dnrm2	(	integer	N,
		double precision, dimension(*)	X,
		integer	INCX
	)

DNRM2

Purpose:

 DNRM2 returns the euclidean norm of a vector via the function
 name, so that

    DNRM2 := sqrt( x'*x )

Parameters

[in]	N	N is INTEGER number of elements in input vector(s)
[in]	X	X is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCX ) )
[in]	INCX	INCX is INTEGER storage spacing between elements of DX

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Further Details:

  -- This version written on 25-October-1982.
     Modified on 14-October-1993 to inline the call to DLASSQ.
     Sven Hammarling, Nag Ltd.

Definition at line 73 of file dnrm2.f.

*
*  -- Reference BLAS level1 routine --
*  -- Reference BLAS is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*
*     .. Scalar Arguments ..
      INTEGER INCX,N
*     ..
*     .. Array Arguments ..
      DOUBLE PRECISION X(*)
*     ..
*
*  =====================================================================
*
*     .. Parameters ..
      DOUBLE PRECISION ONE,ZERO
      parameter(one=1.0d+0,zero=0.0d+0)
*     ..
*     .. Local Scalars ..
      DOUBLE PRECISION ABSXI,NORM,SCALE,SSQ
      INTEGER IX
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC abs,sqrt
*     ..
      IF (n.LT.1 .OR. incx.LT.1) THEN
          norm = zero
      ELSE IF (n.EQ.1) THEN
          norm = abs(x(1))
      ELSE
          scale = zero
          ssq = one
*        The following loop is equivalent to this call to the LAPACK
*        auxiliary routine:
*        CALL DLASSQ( N, X, INCX, SCALE, SSQ )
*
          DO 10 ix = 1,1 + (n-1)*incx,incx
              IF (x(ix).NE.zero) THEN
                  absxi = abs(x(ix))
                  IF (scale.LT.absxi) THEN
                      ssq = one + ssq* (scale/absxi)**2
                      scale = absxi
                  ELSE
                      ssq = ssq + (absxi/scale)**2
                  END IF
              END IF
   10     CONTINUE
          norm = scale*sqrt(ssq)
      END IF
*
      dnrm2 = norm
      RETURN
*
*     End of DNRM2.
*

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