68 lines
1.6 KiB
FortranFixed
68 lines
1.6 KiB
FortranFixed
DOUBLE PRECISION FUNCTION DNRM2(N,X,INCX)
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* .. Scalar Arguments ..
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INTEGER INCX,N
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* ..
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* .. Array Arguments ..
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DOUBLE PRECISION X(*)
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* ..
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*
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* Purpose
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* =======
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*
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* DNRM2 returns the euclidean norm of a vector via the function
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* name, so that
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*
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* DNRM2 := sqrt( x'*x )
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*
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* Further Details
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* ===============
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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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* =====================================================================
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*
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* .. Parameters ..
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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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* ..
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* .. Local Scalars ..
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DOUBLE PRECISION ABSXI,NORM,SCALE,SSQ
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INTEGER IX
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC ABS,SQRT
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* ..
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IF (N.LT.1 .OR. INCX.LT.1) THEN
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NORM = ZERO
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ELSE IF (N.EQ.1) THEN
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NORM = ABS(X(1))
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ELSE
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SCALE = ZERO
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SSQ = ONE
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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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*
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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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SCALE = ABSXI
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ELSE
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SSQ = SSQ + (ABSXI/SCALE)**2
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END IF
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END IF
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10 CONTINUE
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NORM = SCALE*SQRT(SSQ)
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END IF
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*
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DNRM2 = NORM
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RETURN
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*
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* End of DNRM2.
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*
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END
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