DOUBLE PRECISION FUNCTION DNRM2(N,X,INCX) * .. Scalar Arguments .. INTEGER INCX,N * .. * .. Array Arguments .. DOUBLE PRECISION X(*) * .. * * Purpose * ======= * * DNRM2 returns the euclidean norm of a vector via the function * name, so that * * DNRM2 := sqrt( x'*x ) * * Further Details * =============== * * -- This version written on 25-October-1982. * Modified on 14-October-1993 to inline the call to DLASSQ. * Sven Hammarling, Nag Ltd. * * ===================================================================== * * .. 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. * END