ssyconv.f

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*> \brief \b SSYCONV
*
*  =========== DOCUMENTATION ===========
*
* Online html documentation available at 
*            http://www.netlib.org/lapack/explore-html/ 
*
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*> \endhtmlonly 
*
*  Definition:
*  ===========
*
*       SUBROUTINE SSYCONV( UPLO, WAY, N, A, LDA, IPIV, E, INFO )
* 
*       .. Scalar Arguments ..
*       CHARACTER          UPLO, WAY
*       INTEGER            INFO, LDA, N
*       ..
*       .. Array Arguments ..
*       INTEGER            IPIV( * )
*       REAL               A( LDA, * ), E( * )
*       ..
*  
*
*> \par Purpose:
*  =============
*>
*> \verbatim
*>
*> SSYCONV convert A given by TRF into L and D and vice-versa.
*> Get Non-diag elements of D (returned in workspace) and 
*> apply or reverse permutation done in TRF.
*> \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] WAY
*> \verbatim
*>          WAY is CHARACTER*1
*>          = 'C': Convert 
*>          = 'R': Revert
*> \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)
*>          The block diagonal matrix D and the multipliers used to
*>          obtain the factor U or L as computed by SSYTRF.
*> \endverbatim
*>
*> \param[in] LDA
*> \verbatim
*>          LDA is INTEGER
*>          The leading dimension of the array A.  LDA >= max(1,N).
*> \endverbatim
*>
*> \param[in] IPIV
*> \verbatim
*>          IPIV is INTEGER array, dimension (N)
*>          Details of the interchanges and the block structure of D
*>          as determined by SSYTRF.
*> \endverbatim
*>
*> \param[out] E
*> \verbatim
*>          E is REAL array, dimension (N)
*>          E stores the supdiagonal/subdiagonal of the symmetric 1-by-1
*>          or 2-by-2 block diagonal matrix D in LDLT.
*> \endverbatim
*>
*> \param[out] INFO
*> \verbatim
*>          INFO is INTEGER
*>          = 0:  successful exit
*>          < 0:  if INFO = -i, the i-th argument had an illegal value
*> \endverbatim
*
*  Authors:
*  ========
*
*> \author Univ. of Tennessee 
*> \author Univ. of California Berkeley 
*> \author Univ. of Colorado Denver 
*> \author NAG Ltd. 
*
*> \date November 2015
*
*> \ingroup realSYcomputational
*
*  =====================================================================
      SUBROUTINE ssyconv( UPLO, WAY, N, A, LDA, IPIV, E, INFO )
*
*  -- LAPACK computational routine (version 3.6.0) --
*  -- LAPACK is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*     November 2015
*
*     .. Scalar Arguments ..
      CHARACTER          UPLO, WAY
      INTEGER            INFO, LDA, N
*     ..
*     .. Array Arguments ..
      INTEGER            IPIV( * )
      REAL               A( lda, * ), E( * )
*     ..
*
*  =====================================================================
*
*     .. Parameters ..
      REAL               ZERO
      parameter                ( zero = 0.0e+0 )
*     ..
*     .. External Functions ..
      LOGICAL            LSAME
      EXTERNAL           lsame
*
*     .. External Subroutines ..
      EXTERNAL           xerbla
*     .. Local Scalars ..
      LOGICAL            UPPER, CONVERT
      INTEGER            I, IP, J
      REAL               TEMP
*     ..
*     .. Executable Statements ..
*
      info = 0
      upper = lsame( uplo, 'U' )
      convert = lsame( way, 'C' )
      IF( .NOT.upper .AND. .NOT.lsame( uplo, 'L' ) ) THEN
         info = -1
      ELSE IF( .NOT.convert .AND. .NOT.lsame( way, 'R' ) ) THEN
         info = -2
      ELSE IF( n.LT.0 ) THEN
         info = -3
      ELSE IF( lda.LT.max( 1, n ) ) THEN
         info = -5

      END IF
      IF( info.NE.0 ) THEN
         CALL xerbla( 'SSYCONV', -info )
         RETURN
      END IF
*
*     Quick return if possible
*
      IF( n.EQ.0 )
     $   RETURN
*
      IF( upper ) THEN
*
*      A is UPPER
*
*      Convert A (A is upper)
*
*        Convert VALUE
*
         IF ( convert ) THEN
            i=n
            e(1)=zero
            DO WHILE ( i .GT. 1 )
               IF( ipiv(i) .LT. 0 ) THEN
                  e(i)=a(i-1,i)
                  e(i-1)=zero
                  a(i-1,i)=zero
                  i=i-1
               ELSE
                  e(i)=zero
               ENDIF
               i=i-1
            END DO
*
*        Convert PERMUTATIONS
*  
         i=n
         DO WHILE ( i .GE. 1 )
            IF( ipiv(i) .GT. 0) THEN
               ip=ipiv(i)
               IF( i .LT. n) THEN
                  DO 12 j= i+1,n
                    temp=a(ip,j)
                    a(ip,j)=a(i,j)
                    a(i,j)=temp
 12            CONTINUE
               ENDIF
            ELSE
              ip=-ipiv(i)
               IF( i .LT. n) THEN
             DO 13 j= i+1,n
                 temp=a(ip,j)
                 a(ip,j)=a(i-1,j)
                 a(i-1,j)=temp
 13            CONTINUE
                ENDIF
                i=i-1
           ENDIF
           i=i-1
        END DO

         ELSE
*
*      Revert A (A is upper)
*
*
*        Revert PERMUTATIONS
*  
            i=1
            DO WHILE ( i .LE. n )
               IF( ipiv(i) .GT. 0 ) THEN
                  ip=ipiv(i)
                  IF( i .LT. n) THEN
                  DO j= i+1,n
                    temp=a(ip,j)
                    a(ip,j)=a(i,j)
                    a(i,j)=temp
                  END DO
                  ENDIF
               ELSE
                 ip=-ipiv(i)
                 i=i+1
                 IF( i .LT. n) THEN
                    DO j= i+1,n
                       temp=a(ip,j)
                       a(ip,j)=a(i-1,j)
                       a(i-1,j)=temp
                    END DO
                 ENDIF
               ENDIF
               i=i+1
            END DO
*
*        Revert VALUE
*
            i=n
            DO WHILE ( i .GT. 1 )
               IF( ipiv(i) .LT. 0 ) THEN
                  a(i-1,i)=e(i)
                  i=i-1
               ENDIF
               i=i-1
            END DO
         END IF
      ELSE
*
*      A is LOWER
*
         IF ( convert ) THEN
*
*      Convert A (A is lower)
*
*
*        Convert VALUE
*
            i=1
            e(n)=zero
            DO WHILE ( i .LE. n )
               IF( i.LT.n .AND. ipiv(i) .LT. 0 ) THEN
                  e(i)=a(i+1,i)
                  e(i+1)=zero
                  a(i+1,i)=zero
                  i=i+1
               ELSE
                  e(i)=zero
               ENDIF
               i=i+1
            END DO
*
*        Convert PERMUTATIONS
*
         i=1
         DO WHILE ( i .LE. n )
            IF( ipiv(i) .GT. 0 ) THEN
               ip=ipiv(i)
               IF (i .GT. 1) THEN
               DO 22 j= 1,i-1
                 temp=a(ip,j)
                 a(ip,j)=a(i,j)
                 a(i,j)=temp
 22            CONTINUE
               ENDIF
            ELSE
              ip=-ipiv(i)
              IF (i .GT. 1) THEN
              DO 23 j= 1,i-1
                 temp=a(ip,j)
                 a(ip,j)=a(i+1,j)
                 a(i+1,j)=temp
 23           CONTINUE
              ENDIF
              i=i+1
           ENDIF
           i=i+1
        END DO
         ELSE
*
*      Revert A (A is lower)
*
*
*        Revert PERMUTATIONS
*
            i=n
            DO WHILE ( i .GE. 1 )
               IF( ipiv(i) .GT. 0 ) THEN
                  ip=ipiv(i)
                  IF (i .GT. 1) THEN
                     DO j= 1,i-1
                        temp=a(i,j)
                        a(i,j)=a(ip,j)
                        a(ip,j)=temp
                     END DO
                  ENDIF
               ELSE
                  ip=-ipiv(i)
                  i=i-1
                  IF (i .GT. 1) THEN
                     DO j= 1,i-1
                        temp=a(i+1,j)
                        a(i+1,j)=a(ip,j)
                        a(ip,j)=temp
                     END DO
                  ENDIF
               ENDIF
               i=i-1
            END DO
*
*        Revert VALUE
*
            i=1
            DO WHILE ( i .LE. n-1 )
               IF( ipiv(i) .LT. 0 ) THEN
                  a(i+1,i)=e(i)
                  i=i+1
               ENDIF
               i=i+1
            END DO
         END IF
      END IF

      RETURN
*
*     End of SSYCONV
*
      END