60 lines
1.6 KiB
Fortran
60 lines
1.6 KiB
Fortran
REAL FUNCTION SNRM2F ( N, X, INCX )
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* .. Scalar Arguments ..
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INTEGER INCX, N
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* .. Array Arguments ..
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REAL X( * )
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* ..
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*
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* SNRM2 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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* SNRM2 := sqrt( x'*x )
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*
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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 SLASSQ.
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* Sven Hammarling, Nag Ltd.
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*
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*
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* .. Parameters ..
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REAL ONE , ZERO
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PARAMETER ( ONE = 1.0E+0, ZERO = 0.0E+0 )
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* .. Local Scalars ..
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INTEGER IX
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REAL ABSXI, NORM, SCALE, SSQ
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* .. Intrinsic Functions ..
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INTRINSIC ABS, SQRT
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* ..
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* .. Executable Statements ..
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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 SLASSQ( 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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SNRM2F = NORM
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RETURN
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*
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* End of SNRM2.
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*
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END
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