Mercurial > hg > octave-lyh
view libcruft/blas/dznrm2.f @ 6656:c92e679d9cc5
[project @ 2007-05-22 21:20:58 by jwe]
author | jwe |
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date | Tue, 22 May 2007 21:20:58 +0000 |
parents | bac14003d9bb |
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DOUBLE PRECISION FUNCTION DZNRM2( N, X, INCX ) * .. Scalar Arguments .. INTEGER INCX, N * .. Array Arguments .. COMPLEX*16 X( * ) * .. * * DZNRM2 returns the euclidean norm of a vector via the function * name, so that * * DZNRM2 := sqrt( conjg( x' )*x ) * * * * -- This version written on 25-October-1982. * Modified on 14-October-1993 to inline the call to ZLASSQ. * Sven Hammarling, Nag Ltd. * * * .. Parameters .. DOUBLE PRECISION ONE , ZERO PARAMETER ( ONE = 1.0D+0, ZERO = 0.0D+0 ) * .. Local Scalars .. INTEGER IX DOUBLE PRECISION NORM, SCALE, SSQ, TEMP * .. Intrinsic Functions .. INTRINSIC ABS, DIMAG, DBLE, SQRT * .. * .. Executable Statements .. IF( N.LT.1 .OR. INCX.LT.1 )THEN NORM = ZERO ELSE SCALE = ZERO SSQ = ONE * The following loop is equivalent to this call to the LAPACK * auxiliary routine: * CALL ZLASSQ( N, X, INCX, SCALE, SSQ ) * DO 10, IX = 1, 1 + ( N - 1 )*INCX, INCX IF( DBLE( X( IX ) ).NE.ZERO )THEN TEMP = ABS( DBLE( X( IX ) ) ) IF( SCALE.LT.TEMP )THEN SSQ = ONE + SSQ*( SCALE/TEMP )**2 SCALE = TEMP ELSE SSQ = SSQ + ( TEMP/SCALE )**2 END IF END IF IF( DIMAG( X( IX ) ).NE.ZERO )THEN TEMP = ABS( DIMAG( X( IX ) ) ) IF( SCALE.LT.TEMP )THEN SSQ = ONE + SSQ*( SCALE/TEMP )**2 SCALE = TEMP ELSE SSQ = SSQ + ( TEMP/SCALE )**2 END IF END IF 10 CONTINUE NORM = SCALE * SQRT( SSQ ) END IF * DZNRM2 = NORM RETURN * * End of DZNRM2. * END