ssyswapr.f

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*> \brief \b SSYSWAPR applies an elementary permutation on the rows and columns of a symmetric matrix.
*
*  =========== DOCUMENTATION ===========
*
* Online html documentation available at
*            http://www.netlib.org/lapack/explore-html/
*
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*> \endhtmlonly
*
*  Definition:
*  ===========
*
*       SUBROUTINE SSYSWAPR( UPLO, N, A, LDA, I1, I2)
*
*       .. Scalar Arguments ..
*       CHARACTER        UPLO
*       INTEGER          I1, I2, LDA, N
*       ..
*       .. Array Arguments ..
*       REAL             A( LDA, N )
*
*
*> \par Purpose:
*  =============
*>
*> \verbatim
*>
*> SSYSWAPR applies an elementary permutation on the rows and the columns of
*> a symmetric matrix.
*> \endverbatim
*
*  Arguments:
*  ==========
*
*> \param[in] UPLO
*> \verbatim
*>          UPLO is CHARACTER*1
*>          Specifies whether the details of the factorization are stored
*>          as an upper or lower triangular matrix.
*>          = 'U':  Upper triangular, form is A = U*D*U**T;
*>          = 'L':  Lower triangular, form is A = L*D*L**T.
*> \endverbatim
*>
*> \param[in] N
*> \verbatim
*>          N is INTEGER
*>          The order of the matrix A.  N >= 0.
*> \endverbatim
*>
*> \param[in,out] A
*> \verbatim
*>          A is REAL array, dimension (LDA,*)
*>          On entry, the N-by-N matrix A. On exit, the permuted matrix
*>          where the rows I1 and I2 and columns I1 and I2 are interchanged.
*>          If UPLO = 'U', the interchanges are applied to the upper
*>          triangular part and the strictly lower triangular part of A is
*>          not referenced; if UPLO = 'L', the interchanges are applied to
*>          the lower triangular part and the part of A above the diagonal
*>          is not referenced.
*> \endverbatim
*>
*> \param[in] LDA
*> \verbatim
*>          LDA is INTEGER
*>          The leading dimension of the array A.  LDA >= max(1,N).
*> \endverbatim
*>
*> \param[in] I1
*> \verbatim
*>          I1 is INTEGER
*>          Index of the first row to swap
*> \endverbatim
*>
*> \param[in] I2
*> \verbatim
*>          I2 is INTEGER
*>          Index of the second row to swap
*> \endverbatim
*
*  Authors:
*  ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \ingroup realSYauxiliary
*
*  =====================================================================
      SUBROUTINE ssyswapr( UPLO, N, A, LDA, I1, I2)
*
*  -- LAPACK auxiliary routine --
*  -- LAPACK is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*
*     .. Scalar Arguments ..
      CHARACTER        UPLO
      INTEGER          I1, I2, LDA, N
*     ..
*     .. Array Arguments ..
      REAL             A( LDA, * )
*
*  =====================================================================
*
*     ..
*     .. Local Scalars ..
      LOGICAL            UPPER
      REAL               TMP
*
*     .. External Functions ..
      LOGICAL            LSAME
      EXTERNAL           lsame
*     ..
*     .. External Subroutines ..
      EXTERNAL           sswap
*     ..
*     .. Executable Statements ..
*
      upper = lsame( uplo, 'U' )
      IF (upper) THEN
*
*         UPPER
*         first swap
*          - swap column I1 and I2 from I1 to I1-1
         CALL sswap( i1-1, a(1,i1), 1, a(1,i2), 1 )
*
*          second swap :
*          - swap A(I1,I1) and A(I2,I2)
*          - swap row I1 from I1+1 to I2-1 with col I2 from I1+1 to I2-1
         tmp=a(i1,i1)
         a(i1,i1)=a(i2,i2)
         a(i2,i2)=tmp
*
         CALL sswap( i2-i1-1, a(i1,i1+1), lda, a(i1+1,i2), 1 )
*
*          third swap
*          - swap row I1 and I2 from I2+1 to N
         IF ( i2.LT.n )
     $      CALL sswap( n-i2, a(i1,i2+1), lda, a(i2,i2+1), lda )
*
        ELSE
*
*         LOWER
*         first swap
*          - swap row I1 and I2 from I1 to I1-1
         CALL sswap( i1-1, a(i1,1), lda, a(i2,1), lda )
*
*         second swap :
*          - swap A(I1,I1) and A(I2,I2)
*          - swap col I1 from I1+1 to I2-1 with row I2 from I1+1 to I2-1
          tmp=a(i1,i1)
          a(i1,i1)=a(i2,i2)
          a(i2,i2)=tmp
*
          CALL sswap( i2-i1-1, a(i1+1,i1), 1, a(i2,i1+1), lda )
*
*         third swap
*          - swap col I1 and I2 from I2+1 to N
         IF ( i2.LT.n )
     $      CALL sswap( n-i2, a(i2+1,i1), 1, a(i2+1,i2), 1 )
*
      ENDIF
      END SUBROUTINE ssyswapr