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Annotation of rpl/lapack/lapack/dpotri.f, revision 1.7

1.1       bertrand    1:       SUBROUTINE DPOTRI( UPLO, N, A, LDA, INFO )
                      2: *
                      3: *  -- LAPACK routine (version 3.2) --
                      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 2006
                      7: *
                      8: *     .. Scalar Arguments ..
                      9:       CHARACTER          UPLO
                     10:       INTEGER            INFO, LDA, N
                     11: *     ..
                     12: *     .. Array Arguments ..
                     13:       DOUBLE PRECISION   A( LDA, * )
                     14: *     ..
                     15: *
                     16: *  Purpose
                     17: *  =======
                     18: *
                     19: *  DPOTRI computes the inverse of a real symmetric positive definite
                     20: *  matrix A using the Cholesky factorization A = U**T*U or A = L*L**T
                     21: *  computed by DPOTRF.
                     22: *
                     23: *  Arguments
                     24: *  =========
                     25: *
                     26: *  UPLO    (input) CHARACTER*1
                     27: *          = 'U':  Upper triangle of A is stored;
                     28: *          = 'L':  Lower triangle of A is stored.
                     29: *
                     30: *  N       (input) INTEGER
                     31: *          The order of the matrix A.  N >= 0.
                     32: *
                     33: *  A       (input/output) DOUBLE PRECISION array, dimension (LDA,N)
                     34: *          On entry, the triangular factor U or L from the Cholesky
                     35: *          factorization A = U**T*U or A = L*L**T, as computed by
                     36: *          DPOTRF.
                     37: *          On exit, the upper or lower triangle of the (symmetric)
                     38: *          inverse of A, overwriting the input factor U or L.
                     39: *
                     40: *  LDA     (input) INTEGER
                     41: *          The leading dimension of the array A.  LDA >= max(1,N).
                     42: *
                     43: *  INFO    (output) INTEGER
                     44: *          = 0:  successful exit
                     45: *          < 0:  if INFO = -i, the i-th argument had an illegal value
                     46: *          > 0:  if INFO = i, the (i,i) element of the factor U or L is
                     47: *                zero, and the inverse could not be computed.
                     48: *
                     49: *  =====================================================================
                     50: *
                     51: *     .. External Functions ..
                     52:       LOGICAL            LSAME
                     53:       EXTERNAL           LSAME
                     54: *     ..
                     55: *     .. External Subroutines ..
                     56:       EXTERNAL           DLAUUM, DTRTRI, XERBLA
                     57: *     ..
                     58: *     .. Intrinsic Functions ..
                     59:       INTRINSIC          MAX
                     60: *     ..
                     61: *     .. Executable Statements ..
                     62: *
                     63: *     Test the input parameters.
                     64: *
                     65:       INFO = 0
                     66:       IF( .NOT.LSAME( UPLO, 'U' ) .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
                     67:          INFO = -1
                     68:       ELSE IF( N.LT.0 ) THEN
                     69:          INFO = -2
                     70:       ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
                     71:          INFO = -4
                     72:       END IF
                     73:       IF( INFO.NE.0 ) THEN
                     74:          CALL XERBLA( 'DPOTRI', -INFO )
                     75:          RETURN
                     76:       END IF
                     77: *
                     78: *     Quick return if possible
                     79: *
                     80:       IF( N.EQ.0 )
                     81:      $   RETURN
                     82: *
                     83: *     Invert the triangular Cholesky factor U or L.
                     84: *
                     85:       CALL DTRTRI( UPLO, 'Non-unit', N, A, LDA, INFO )
                     86:       IF( INFO.GT.0 )
                     87:      $   RETURN
                     88: *
                     89: *     Form inv(U)*inv(U)' or inv(L)'*inv(L).
                     90: *
                     91:       CALL DLAUUM( UPLO, N, A, LDA, INFO )
                     92: *
                     93:       RETURN
                     94: *
                     95: *     End of DPOTRI
                     96: *
                     97:       END