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DOUBLE PRECISION FUNCTION DNRM2 ( N, X, INCX )
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* $Id: dnrm2.f 19695 2010-10-29 16:51:02Z d3y133 $
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* =========== DOCUMENTATION ===========
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* Online html documentation available at
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* http://www.netlib.org/lapack/explore-html/
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* DOUBLE PRECISION FUNCTION DNRM2(N,X,INCX)
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* .. Scalar Arguments ..
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* .. Array Arguments ..
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* DOUBLE PRECISION X(*)
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*> DNRM2 returns the euclidean norm of a vector via the function
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*> DNRM2 := sqrt( x'*x )
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*> \author Univ. of Tennessee
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*> \author Univ. of California Berkeley
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*> \author Univ. of Colorado Denver
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*> \date November 2011
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*> \ingroup double_blas_level1
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*> \par Further Details:
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* =====================
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*> -- This version written on 25-October-1982.
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*> Modified on 14-October-1993 to inline the call to DLASSQ.
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*> Sven Hammarling, Nag Ltd.
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* =====================================================================
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DOUBLE PRECISION FUNCTION DNRM2(N,X,INCX)
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* -- Reference BLAS level1 routine (version 3.4.0) --
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* -- Reference BLAS is a software package provided by Univ. of Tennessee, --
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* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
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* .. Scalar Arguments ..
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* .. Array Arguments ..
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DOUBLE PRECISION X( * )
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* DNRM2 returns the euclidean norm of a vector via the function
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* DNRM2 := sqrt( x'*x )
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* -- This version written on 25-October-1982.
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* Modified on 14-October-1993 to inline the call to DLASSQ.
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* Sven Hammarling, Nag Ltd.
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* =====================================================================
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DOUBLE PRECISION ONE , ZERO
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PARAMETER ( ONE = 1.0D+0, ZERO = 0.0D+0 )
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DOUBLE PRECISION ONE,ZERO
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PARAMETER (ONE=1.0D+0,ZERO=0.0D+0)
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* .. Local Scalars ..
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DOUBLE PRECISION ABSXI, NORM, SCALE, SSQ
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DOUBLE PRECISION ABSXI,NORM,SCALE,SSQ
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* .. Intrinsic Functions ..
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* .. Executable Statements ..
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IF( N.LT.1 .OR. INCX.LT.1 )THEN
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IF (N.LT.1 .OR. INCX.LT.1) THEN
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* The following loop is equivalent to this call to the LAPACK
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* auxiliary routine:
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* CALL DLASSQ( N, X, INCX, SCALE, SSQ )
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DO 10, IX = 1, 1 + ( N - 1 )*INCX, INCX
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IF( X( IX ).NE.ZERO )THEN
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ABSXI = ABS( X( IX ) )
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IF( SCALE.LT.ABSXI )THEN
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SSQ = ONE + SSQ*( SCALE/ABSXI )**2
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SSQ = SSQ + ( ABSXI/SCALE )**2
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NORM = SCALE * SQRT( SSQ )
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DO 10 IX = 1,1 + (N-1)*INCX,INCX
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IF (X(IX).NE.ZERO) THEN
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IF (SCALE.LT.ABSXI) THEN
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SSQ = ONE + SSQ* (SCALE/ABSXI)**2
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SSQ = SSQ + (ABSXI/SCALE)**2
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NORM = SCALE*SQRT(SSQ)