LAPACK  3.4.1
LAPACK: Linear Algebra PACKage
spotri.f
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00001 *> \brief \b SPOTRI
00002 *
00003 *  =========== DOCUMENTATION ===========
00004 *
00005 * Online html documentation available at 
00006 *            http://www.netlib.org/lapack/explore-html/ 
00007 *
00008 *> \htmlonly
00009 *> Download SPOTRI + dependencies 
00010 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/spotri.f"> 
00011 *> [TGZ]</a> 
00012 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/spotri.f"> 
00013 *> [ZIP]</a> 
00014 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/spotri.f"> 
00015 *> [TXT]</a>
00016 *> \endhtmlonly 
00017 *
00018 *  Definition:
00019 *  ===========
00020 *
00021 *       SUBROUTINE SPOTRI( UPLO, N, A, LDA, INFO )
00022 * 
00023 *       .. Scalar Arguments ..
00024 *       CHARACTER          UPLO
00025 *       INTEGER            INFO, LDA, N
00026 *       ..
00027 *       .. Array Arguments ..
00028 *       REAL               A( LDA, * )
00029 *       ..
00030 *  
00031 *
00032 *> \par Purpose:
00033 *  =============
00034 *>
00035 *> \verbatim
00036 *>
00037 *> SPOTRI computes the inverse of a real symmetric positive definite
00038 *> matrix A using the Cholesky factorization A = U**T*U or A = L*L**T
00039 *> computed by SPOTRF.
00040 *> \endverbatim
00041 *
00042 *  Arguments:
00043 *  ==========
00044 *
00045 *> \param[in] UPLO
00046 *> \verbatim
00047 *>          UPLO is CHARACTER*1
00048 *>          = 'U':  Upper triangle of A is stored;
00049 *>          = 'L':  Lower triangle of A is stored.
00050 *> \endverbatim
00051 *>
00052 *> \param[in] N
00053 *> \verbatim
00054 *>          N is INTEGER
00055 *>          The order of the matrix A.  N >= 0.
00056 *> \endverbatim
00057 *>
00058 *> \param[in,out] A
00059 *> \verbatim
00060 *>          A is REAL array, dimension (LDA,N)
00061 *>          On entry, the triangular factor U or L from the Cholesky
00062 *>          factorization A = U**T*U or A = L*L**T, as computed by
00063 *>          SPOTRF.
00064 *>          On exit, the upper or lower triangle of the (symmetric)
00065 *>          inverse of A, overwriting the input factor U or L.
00066 *> \endverbatim
00067 *>
00068 *> \param[in] LDA
00069 *> \verbatim
00070 *>          LDA is INTEGER
00071 *>          The leading dimension of the array A.  LDA >= max(1,N).
00072 *> \endverbatim
00073 *>
00074 *> \param[out] INFO
00075 *> \verbatim
00076 *>          INFO is INTEGER
00077 *>          = 0:  successful exit
00078 *>          < 0:  if INFO = -i, the i-th argument had an illegal value
00079 *>          > 0:  if INFO = i, the (i,i) element of the factor U or L is
00080 *>                zero, and the inverse could not be computed.
00081 *> \endverbatim
00082 *
00083 *  Authors:
00084 *  ========
00085 *
00086 *> \author Univ. of Tennessee 
00087 *> \author Univ. of California Berkeley 
00088 *> \author Univ. of Colorado Denver 
00089 *> \author NAG Ltd. 
00090 *
00091 *> \date November 2011
00092 *
00093 *> \ingroup realPOcomputational
00094 *
00095 *  =====================================================================
00096       SUBROUTINE SPOTRI( UPLO, N, A, LDA, INFO )
00097 *
00098 *  -- LAPACK computational routine (version 3.4.0) --
00099 *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
00100 *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
00101 *     November 2011
00102 *
00103 *     .. Scalar Arguments ..
00104       CHARACTER          UPLO
00105       INTEGER            INFO, LDA, N
00106 *     ..
00107 *     .. Array Arguments ..
00108       REAL               A( LDA, * )
00109 *     ..
00110 *
00111 *  =====================================================================
00112 *
00113 *     .. External Functions ..
00114       LOGICAL            LSAME
00115       EXTERNAL           LSAME
00116 *     ..
00117 *     .. External Subroutines ..
00118       EXTERNAL           SLAUUM, STRTRI, XERBLA
00119 *     ..
00120 *     .. Intrinsic Functions ..
00121       INTRINSIC          MAX
00122 *     ..
00123 *     .. Executable Statements ..
00124 *
00125 *     Test the input parameters.
00126 *
00127       INFO = 0
00128       IF( .NOT.LSAME( UPLO, 'U' ) .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
00129          INFO = -1
00130       ELSE IF( N.LT.0 ) THEN
00131          INFO = -2
00132       ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
00133          INFO = -4
00134       END IF
00135       IF( INFO.NE.0 ) THEN
00136          CALL XERBLA( 'SPOTRI', -INFO )
00137          RETURN
00138       END IF
00139 *
00140 *     Quick return if possible
00141 *
00142       IF( N.EQ.0 )
00143      $   RETURN
00144 *
00145 *     Invert the triangular Cholesky factor U or L.
00146 *
00147       CALL STRTRI( UPLO, 'Non-unit', N, A, LDA, INFO )
00148       IF( INFO.GT.0 )
00149      $   RETURN
00150 *
00151 *     Form inv(U) * inv(U)**T or inv(L)**T * inv(L).
00152 *
00153       CALL SLAUUM( UPLO, N, A, LDA, INFO )
00154 *
00155       RETURN
00156 *
00157 *     End of SPOTRI
00158 *
00159       END
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