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161 lines
3.9 KiB
161 lines
3.9 KiB
*> \brief \b DSXT1
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*
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* =========== DOCUMENTATION ===========
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*
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* Online html documentation available at
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* http://www.netlib.org/lapack/explore-html/
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*
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* Definition:
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* ===========
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*
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* DOUBLE PRECISION FUNCTION DSXT1( IJOB, D1, N1, D2, N2, ABSTOL,
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* ULP, UNFL )
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*
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* .. Scalar Arguments ..
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* INTEGER IJOB, N1, N2
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* DOUBLE PRECISION ABSTOL, ULP, UNFL
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* ..
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* .. Array Arguments ..
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* DOUBLE PRECISION D1( * ), D2( * )
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* ..
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*
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*
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*> \par Purpose:
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* =============
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*>
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*> \verbatim
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*>
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*> DSXT1 computes the difference between a set of eigenvalues.
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*> The result is returned as the function value.
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*>
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*> IJOB = 1: Computes max { min | D1(i)-D2(j) | }
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*> i j
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*>
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*> IJOB = 2: Computes max { min | D1(i)-D2(j) | /
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*> i j
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*> ( ABSTOL + |D1(i)|*ULP ) }
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*> \endverbatim
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*
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* Arguments:
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* ==========
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*
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*> \param[in] IJOB
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*> \verbatim
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*> IJOB is INTEGER
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*> Specifies the type of tests to be performed. (See above.)
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*> \endverbatim
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*>
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*> \param[in] D1
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*> \verbatim
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*> D1 is DOUBLE PRECISION array, dimension (N1)
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*> The first array. D1 should be in increasing order, i.e.,
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*> D1(j) <= D1(j+1).
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*> \endverbatim
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*>
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*> \param[in] N1
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*> \verbatim
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*> N1 is INTEGER
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*> The length of D1.
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*> \endverbatim
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*>
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*> \param[in] D2
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*> \verbatim
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*> D2 is DOUBLE PRECISION array, dimension (N2)
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*> The second array. D2 should be in increasing order, i.e.,
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*> D2(j) <= D2(j+1).
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*> \endverbatim
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*>
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*> \param[in] N2
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*> \verbatim
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*> N2 is INTEGER
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*> The length of D2.
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*> \endverbatim
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*>
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*> \param[in] ABSTOL
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*> \verbatim
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*> ABSTOL is DOUBLE PRECISION
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*> The absolute tolerance, used as a measure of the error.
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*> \endverbatim
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*>
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*> \param[in] ULP
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*> \verbatim
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*> ULP is DOUBLE PRECISION
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*> Machine precision.
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*> \endverbatim
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*>
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*> \param[in] UNFL
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*> \verbatim
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*> UNFL is DOUBLE PRECISION
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*> The smallest positive number whose reciprocal does not
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*> overflow.
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*> \endverbatim
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*
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* Authors:
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* ========
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*
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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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*> \author NAG Ltd.
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*
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*> \ingroup double_eig
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*
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* =====================================================================
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DOUBLE PRECISION FUNCTION DSXT1( IJOB, D1, N1, D2, N2, ABSTOL,
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$ ULP, UNFL )
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*
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* -- LAPACK test routine --
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* -- LAPACK 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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*
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* .. Scalar Arguments ..
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INTEGER IJOB, N1, N2
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DOUBLE PRECISION ABSTOL, ULP, UNFL
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* ..
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* .. Array Arguments ..
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DOUBLE PRECISION D1( * ), D2( * )
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* ..
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*
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* =====================================================================
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*
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* .. Parameters ..
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DOUBLE PRECISION ZERO
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PARAMETER ( ZERO = 0.0D0 )
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* ..
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* .. Local Scalars ..
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INTEGER I, J
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DOUBLE PRECISION TEMP1, TEMP2
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC ABS, MAX, MIN
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* ..
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* .. Executable Statements ..
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*
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TEMP1 = ZERO
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*
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J = 1
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DO 20 I = 1, N1
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10 CONTINUE
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IF( D2( J ).LT.D1( I ) .AND. J.LT.N2 ) THEN
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J = J + 1
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GO TO 10
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END IF
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IF( J.EQ.1 ) THEN
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TEMP2 = ABS( D2( J )-D1( I ) )
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IF( IJOB.EQ.2 )
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$ TEMP2 = TEMP2 / MAX( UNFL, ABSTOL+ULP*ABS( D1( I ) ) )
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ELSE
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TEMP2 = MIN( ABS( D2( J )-D1( I ) ),
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$ ABS( D1( I )-D2( J-1 ) ) )
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IF( IJOB.EQ.2 )
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$ TEMP2 = TEMP2 / MAX( UNFL, ABSTOL+ULP*ABS( D1( I ) ) )
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END IF
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TEMP1 = MAX( TEMP1, TEMP2 )
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20 CONTINUE
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*
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DSXT1 = TEMP1
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RETURN
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*
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* End of DSXT1
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*
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END
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