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,N)
*>          On entry, the NB diagonal matrix D and the multipliers
*>          used to obtain the factor U or L as computed by SSYTRF.
*>
*>          On exit, if INFO = 0, the (symmetric) inverse of the original
*>          matrix.  If UPLO = 'U', the upper triangular part of the
*>          inverse is formed and the part of A below the diagonal is not
*>          referenced; if UPLO = 'L' the lower triangular part of the
*>          inverse is formed 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, N )
*
*  =====================================================================
*
*     ..
*     .. Local Scalars ..
      LOGICAL            UPPER
      INTEGER            I
      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
*
         DO i=1,i2-i1-1
            tmp=a(i1,i1+i)
            a(i1,i1+i)=a(i1+i,i2)
            a(i1+i,i2)=tmp
         END DO
*
*          third swap
*          - swap row I1 and I2 from I2+1 to N
         DO i=i2+1,n
            tmp=a(i1,i)
            a(i1,i)=a(i2,i)
            a(i2,i)=tmp
         END DO
*
        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
*
          DO i=1,i2-i1-1
             tmp=a(i1+i,i1)
             a(i1+i,i1)=a(i2,i1+i)
             a(i2,i1+i)=tmp
          END DO
*
*         third swap
*          - swap col I1 and I2 from I2+1 to N
          DO i=i2+1,n
             tmp=a(i,i1)
             a(i,i1)=a(i,i2)
             a(i,i2)=tmp
          END DO
*
      ENDIF
      END SUBROUTINE ssyswapr