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Annotation of rpl/lapack/lapack/dsytri2.f, revision 1.2

1.1       bertrand    1:       SUBROUTINE DSYTRI2( UPLO, N, A, LDA, IPIV, WORK, LWORK, INFO )
                      2: *
                      3: *  -- LAPACK routine (version 3.3.0) --
                      4: *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
                      5: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
                      6: *     November 2010
                      7: *
                      8: *  -- Written by Julie Langou of the Univ. of TN    --
                      9: *
                     10: *     .. Scalar Arguments ..
                     11:       CHARACTER          UPLO
                     12:       INTEGER            INFO, LDA, LWORK, N
                     13: *     ..
                     14: *     .. Array Arguments ..
                     15:       INTEGER            IPIV( * )
                     16:       DOUBLE PRECISION   A( LDA, * ), WORK( * )
                     17: *     ..
                     18: *
                     19: *  Purpose
                     20: *  =======
                     21: *
                     22: *  DSYTRI2 computes the inverse of a real symmetric indefinite matrix
                     23: *  A using the factorization A = U*D*U**T or A = L*D*L**T computed by
                     24: *  DSYTRF. DSYTRI2 sets the LEADING DIMENSION of the workspace
                     25: *  before calling DSYTRI2X that actually computes the inverse.
                     26: *
                     27: *  Arguments
                     28: *  =========
                     29: *
                     30: *  UPLO    (input) CHARACTER*1
                     31: *          Specifies whether the details of the factorization are stored
                     32: *          as an upper or lower triangular matrix.
                     33: *          = 'U':  Upper triangular, form is A = U*D*U**T;
                     34: *          = 'L':  Lower triangular, form is A = L*D*L**T.
                     35: *
                     36: *  N       (input) INTEGER
                     37: *          The order of the matrix A.  N >= 0.
                     38: *
                     39: *  A       (input/output) DOUBLE PRECISION array, dimension (LDA,N)
                     40: *          On entry, the NB diagonal matrix D and the multipliers
                     41: *          used to obtain the factor U or L as computed by DSYTRF.
                     42: *
                     43: *          On exit, if INFO = 0, the (symmetric) inverse of the original
                     44: *          matrix.  If UPLO = 'U', the upper triangular part of the
                     45: *          inverse is formed and the part of A below the diagonal is not
                     46: *          referenced; if UPLO = 'L' the lower triangular part of the
                     47: *          inverse is formed and the part of A above the diagonal is
                     48: *          not referenced.
                     49: *
                     50: *  LDA     (input) INTEGER
                     51: *          The leading dimension of the array A.  LDA >= max(1,N).
                     52: *
                     53: *  IPIV    (input) INTEGER array, dimension (N)
                     54: *          Details of the interchanges and the NB structure of D
                     55: *          as determined by DSYTRF.
                     56: *
                     57: *  WORK    (workspace) DOUBLE PRECISION array, dimension (N+NB+1)*(NB+3)
                     58: *
                     59: *  LWORK   (input) INTEGER
                     60: *          The dimension of the array WORK.
                     61: *          WORK is size >= (N+NB+1)*(NB+3)
                     62: *          If LDWORK = -1, then a workspace query is assumed; the routine
                     63: *           calculates:
                     64: *              - the optimal size of the WORK array, returns
                     65: *          this value as the first entry of the WORK array,
                     66: *              - and no error message related to LDWORK is issued by XERBLA.
                     67: *
                     68: *  INFO    (output) INTEGER
                     69: *          = 0: successful exit
                     70: *          < 0: if INFO = -i, the i-th argument had an illegal value
                     71: *          > 0: if INFO = i, D(i,i) = 0; the matrix is singular and its
                     72: *               inverse could not be computed.
                     73: *
                     74: *  =====================================================================
                     75: *
                     76: *     .. Local Scalars ..
                     77:       LOGICAL            UPPER, LQUERY
                     78:       INTEGER            MINSIZE, NBMAX
                     79: *     ..
                     80: *     .. External Functions ..
                     81:       LOGICAL            LSAME
                     82:       INTEGER            ILAENV
                     83:       EXTERNAL           LSAME, ILAENV
                     84: *     ..
                     85: *     .. External Subroutines ..
                     86:       EXTERNAL           DSYTRI2X
                     87: *     ..
                     88: *     .. Executable Statements ..
                     89: *
                     90: *     Test the input parameters.
                     91: *
                     92:       INFO = 0
                     93:       UPPER = LSAME( UPLO, 'U' )
                     94:       LQUERY = ( LWORK.EQ.-1 )
                     95: *     Get blocksize
                     96:       NBMAX = ILAENV( 1, 'DSYTRF', UPLO, N, -1, -1, -1 )
                     97:       MINSIZE = (N+NBMAX+1)*(NBMAX+3)
                     98: *
                     99:       IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
                    100:          INFO = -1
                    101:       ELSE IF( N.LT.0 ) THEN
                    102:          INFO = -2
                    103:       ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
                    104:          INFO = -4
                    105:       ELSE IF (LWORK .LT. MINSIZE .AND. .NOT.LQUERY ) THEN
                    106:          INFO = -7
                    107:       END IF
                    108: *
                    109: *     Quick return if possible
                    110: *
                    111: *
                    112:       IF( INFO.NE.0 ) THEN
                    113:          CALL XERBLA( 'DSYTRI2', -INFO )
                    114:          RETURN
                    115:       ELSE IF( LQUERY ) THEN
                    116:          WORK(1)=(N+NBMAX+1)*(NBMAX+3)
                    117:          RETURN
                    118:       END IF
                    119:       IF( N.EQ.0 )
                    120:      $   RETURN
                    121:       
                    122:       CALL DSYTRI2X( UPLO, N, A, LDA, IPIV, WORK, NBMAX, INFO )
                    123:       RETURN
                    124: *
                    125: *     End of DSYTRI2
                    126: *
                    127:       END