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174 lines
4.8 KiB
174 lines
4.8 KiB
2 years ago
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*> \brief \b DSYSWAPR applies an elementary permutation on the rows and columns of a symmetric matrix.
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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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*> \htmlonly
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*> Download DSYSWAPR + dependencies
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dsyswapr.f">
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*> [TGZ]</a>
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dsyswapr.f">
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*> [ZIP]</a>
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dsyswapr.f">
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*> [TXT]</a>
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*> \endhtmlonly
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*
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* Definition:
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* ===========
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*
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* SUBROUTINE DSYSWAPR( UPLO, N, A, LDA, I1, I2)
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*
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* .. Scalar Arguments ..
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* CHARACTER UPLO
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* INTEGER I1, I2, LDA, N
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* ..
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* .. Array Arguments ..
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* DOUBLE PRECISION A( LDA, N )
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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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*> DSYSWAPR applies an elementary permutation on the rows and the columns of
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*> a symmetric matrix.
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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] UPLO
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*> \verbatim
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*> UPLO is CHARACTER*1
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*> Specifies whether the details of the factorization are stored
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*> as an upper or lower triangular matrix.
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*> = 'U': Upper triangular, form is A = U*D*U**T;
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*> = 'L': Lower triangular, form is A = L*D*L**T.
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*> \endverbatim
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*>
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*> \param[in] N
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*> \verbatim
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*> N is INTEGER
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*> The order of the matrix A. N >= 0.
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*> \endverbatim
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*>
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*> \param[in,out] A
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*> \verbatim
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*> A is DOUBLE PRECISION array, dimension (LDA,*)
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*> On entry, the N-by-N matrix A. On exit, the permuted matrix
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*> where the rows I1 and I2 and columns I1 and I2 are interchanged.
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*> If UPLO = 'U', the interchanges are applied to the upper
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*> triangular part and the strictly lower triangular part of A is
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*> not referenced; if UPLO = 'L', the interchanges are applied to
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*> the lower triangular part and the part of A above the diagonal
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*> is not referenced.
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*> \endverbatim
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*>
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*> \param[in] LDA
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*> \verbatim
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*> LDA is INTEGER
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*> The leading dimension of the array A. LDA >= max(1,N).
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*> \endverbatim
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*>
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*> \param[in] I1
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*> \verbatim
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*> I1 is INTEGER
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*> Index of the first row to swap
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*> \endverbatim
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*>
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*> \param[in] I2
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*> \verbatim
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*> I2 is INTEGER
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*> Index of the second row to swap
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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 doubleSYauxiliary
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*
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* =====================================================================
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SUBROUTINE DSYSWAPR( UPLO, N, A, LDA, I1, I2)
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*
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* -- LAPACK auxiliary 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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CHARACTER UPLO
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INTEGER I1, I2, LDA, N
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* ..
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* .. Array Arguments ..
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DOUBLE PRECISION A( LDA, * )
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*
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* =====================================================================
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*
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* ..
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* .. Local Scalars ..
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LOGICAL UPPER
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DOUBLE PRECISION TMP
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*
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* .. External Functions ..
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LOGICAL LSAME
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EXTERNAL LSAME
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* ..
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* .. External Subroutines ..
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EXTERNAL DSWAP
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* ..
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* .. Executable Statements ..
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*
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UPPER = LSAME( UPLO, 'U' )
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IF (UPPER) THEN
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*
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* UPPER
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* first swap
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* - swap column I1 and I2 from I1 to I1-1
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CALL DSWAP( I1-1, A(1,I1), 1, A(1,I2), 1 )
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*
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* second swap :
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* - swap A(I1,I1) and A(I2,I2)
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* - swap row I1 from I1+1 to I2-1 with col I2 from I1+1 to I2-1
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TMP=A(I1,I1)
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A(I1,I1)=A(I2,I2)
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A(I2,I2)=TMP
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*
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CALL DSWAP( I2-I1-1, A(I1,I1+1), LDA, A(I1+1,I2), 1 )
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*
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* third swap
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* - swap row I1 and I2 from I2+1 to N
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IF ( I2.LT.N )
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$ CALL DSWAP( N-I2, A(I1,I2+1), LDA, A(I2,I2+1), LDA )
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*
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ELSE
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*
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* LOWER
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* first swap
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* - swap row I1 and I2 from I1 to I1-1
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CALL DSWAP( I1-1, A(I1,1), LDA, A(I2,1), LDA )
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*
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* second swap :
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* - swap A(I1,I1) and A(I2,I2)
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* - swap col I1 from I1+1 to I2-1 with row I2 from I1+1 to I2-1
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TMP=A(I1,I1)
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A(I1,I1)=A(I2,I2)
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A(I2,I2)=TMP
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*
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CALL DSWAP( I2-I1-1, A(I1+1,I1), 1, A(I2,I1+1), LDA )
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*
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* third swap
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* - swap col I1 and I2 from I2+1 to N
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IF ( I2.LT.N )
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$ CALL DSWAP( N-I2, A(I2+1,I1), 1, A(I2+1,I2), 1 )
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*
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ENDIF
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END SUBROUTINE DSYSWAPR
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