LAPACK  3.4.1
LAPACK: Linear Algebra PACKage
dtptrs.f
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00001 *> \brief \b DTPTRS
00002 *
00003 *  =========== DOCUMENTATION ===========
00004 *
00005 * Online html documentation available at 
00006 *            http://www.netlib.org/lapack/explore-html/ 
00007 *
00008 *> \htmlonly
00009 *> Download DTPTRS + dependencies 
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00011 *> [TGZ]</a> 
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00013 *> [ZIP]</a> 
00014 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dtptrs.f"> 
00015 *> [TXT]</a>
00016 *> \endhtmlonly 
00017 *
00018 *  Definition:
00019 *  ===========
00020 *
00021 *       SUBROUTINE DTPTRS( UPLO, TRANS, DIAG, N, NRHS, AP, B, LDB, INFO )
00022 * 
00023 *       .. Scalar Arguments ..
00024 *       CHARACTER          DIAG, TRANS, UPLO
00025 *       INTEGER            INFO, LDB, N, NRHS
00026 *       ..
00027 *       .. Array Arguments ..
00028 *       DOUBLE PRECISION   AP( * ), B( LDB, * )
00029 *       ..
00030 *  
00031 *
00032 *> \par Purpose:
00033 *  =============
00034 *>
00035 *> \verbatim
00036 *>
00037 *> DTPTRS solves a triangular system of the form
00038 *>
00039 *>    A * X = B  or  A**T * X = B,
00040 *>
00041 *> where A is a triangular matrix of order N stored in packed format,
00042 *> and B is an N-by-NRHS matrix.  A check is made to verify that A is
00043 *> nonsingular.
00044 *> \endverbatim
00045 *
00046 *  Arguments:
00047 *  ==========
00048 *
00049 *> \param[in] UPLO
00050 *> \verbatim
00051 *>          UPLO is CHARACTER*1
00052 *>          = 'U':  A is upper triangular;
00053 *>          = 'L':  A is lower triangular.
00054 *> \endverbatim
00055 *>
00056 *> \param[in] TRANS
00057 *> \verbatim
00058 *>          TRANS is CHARACTER*1
00059 *>          Specifies the form of the system of equations:
00060 *>          = 'N':  A * X = B  (No transpose)
00061 *>          = 'T':  A**T * X = B  (Transpose)
00062 *>          = 'C':  A**H * X = B  (Conjugate transpose = Transpose)
00063 *> \endverbatim
00064 *>
00065 *> \param[in] DIAG
00066 *> \verbatim
00067 *>          DIAG is CHARACTER*1
00068 *>          = 'N':  A is non-unit triangular;
00069 *>          = 'U':  A is unit triangular.
00070 *> \endverbatim
00071 *>
00072 *> \param[in] N
00073 *> \verbatim
00074 *>          N is INTEGER
00075 *>          The order of the matrix A.  N >= 0.
00076 *> \endverbatim
00077 *>
00078 *> \param[in] NRHS
00079 *> \verbatim
00080 *>          NRHS is INTEGER
00081 *>          The number of right hand sides, i.e., the number of columns
00082 *>          of the matrix B.  NRHS >= 0.
00083 *> \endverbatim
00084 *>
00085 *> \param[in] AP
00086 *> \verbatim
00087 *>          AP is DOUBLE PRECISION array, dimension (N*(N+1)/2)
00088 *>          The upper or lower triangular matrix A, packed columnwise in
00089 *>          a linear array.  The j-th column of A is stored in the array
00090 *>          AP as follows:
00091 *>          if UPLO = 'U', AP(i + (j-1)*j/2) = A(i,j) for 1<=i<=j;
00092 *>          if UPLO = 'L', AP(i + (j-1)*(2*n-j)/2) = A(i,j) for j<=i<=n.
00093 *> \endverbatim
00094 *>
00095 *> \param[in,out] B
00096 *> \verbatim
00097 *>          B is DOUBLE PRECISION array, dimension (LDB,NRHS)
00098 *>          On entry, the right hand side matrix B.
00099 *>          On exit, if INFO = 0, the solution matrix X.
00100 *> \endverbatim
00101 *>
00102 *> \param[in] LDB
00103 *> \verbatim
00104 *>          LDB is INTEGER
00105 *>          The leading dimension of the array B.  LDB >= max(1,N).
00106 *> \endverbatim
00107 *>
00108 *> \param[out] INFO
00109 *> \verbatim
00110 *>          INFO is INTEGER
00111 *>          = 0:  successful exit
00112 *>          < 0:  if INFO = -i, the i-th argument had an illegal value
00113 *>          > 0:  if INFO = i, the i-th diagonal element of A is zero,
00114 *>                indicating that the matrix is singular and the
00115 *>                solutions X have not been computed.
00116 *> \endverbatim
00117 *
00118 *  Authors:
00119 *  ========
00120 *
00121 *> \author Univ. of Tennessee 
00122 *> \author Univ. of California Berkeley 
00123 *> \author Univ. of Colorado Denver 
00124 *> \author NAG Ltd. 
00125 *
00126 *> \date November 2011
00127 *
00128 *> \ingroup doubleOTHERcomputational
00129 *
00130 *  =====================================================================
00131       SUBROUTINE DTPTRS( UPLO, TRANS, DIAG, N, NRHS, AP, B, LDB, INFO )
00132 *
00133 *  -- LAPACK computational routine (version 3.4.0) --
00134 *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
00135 *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
00136 *     November 2011
00137 *
00138 *     .. Scalar Arguments ..
00139       CHARACTER          DIAG, TRANS, UPLO
00140       INTEGER            INFO, LDB, N, NRHS
00141 *     ..
00142 *     .. Array Arguments ..
00143       DOUBLE PRECISION   AP( * ), B( LDB, * )
00144 *     ..
00145 *
00146 *  =====================================================================
00147 *
00148 *     .. Parameters ..
00149       DOUBLE PRECISION   ZERO
00150       PARAMETER          ( ZERO = 0.0D+0 )
00151 *     ..
00152 *     .. Local Scalars ..
00153       LOGICAL            NOUNIT, UPPER
00154       INTEGER            J, JC
00155 *     ..
00156 *     .. External Functions ..
00157       LOGICAL            LSAME
00158       EXTERNAL           LSAME
00159 *     ..
00160 *     .. External Subroutines ..
00161       EXTERNAL           DTPSV, XERBLA
00162 *     ..
00163 *     .. Intrinsic Functions ..
00164       INTRINSIC          MAX
00165 *     ..
00166 *     .. Executable Statements ..
00167 *
00168 *     Test the input parameters.
00169 *
00170       INFO = 0
00171       UPPER = LSAME( UPLO, 'U' )
00172       NOUNIT = LSAME( DIAG, 'N' )
00173       IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
00174          INFO = -1
00175       ELSE IF( .NOT.LSAME( TRANS, 'N' ) .AND. .NOT.
00176      $         LSAME( TRANS, 'T' ) .AND. .NOT.LSAME( TRANS, 'C' ) ) THEN
00177          INFO = -2
00178       ELSE IF( .NOT.NOUNIT .AND. .NOT.LSAME( DIAG, 'U' ) ) THEN
00179          INFO = -3
00180       ELSE IF( N.LT.0 ) THEN
00181          INFO = -4
00182       ELSE IF( NRHS.LT.0 ) THEN
00183          INFO = -5
00184       ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
00185          INFO = -8
00186       END IF
00187       IF( INFO.NE.0 ) THEN
00188          CALL XERBLA( 'DTPTRS', -INFO )
00189          RETURN
00190       END IF
00191 *
00192 *     Quick return if possible
00193 *
00194       IF( N.EQ.0 )
00195      $   RETURN
00196 *
00197 *     Check for singularity.
00198 *
00199       IF( NOUNIT ) THEN
00200          IF( UPPER ) THEN
00201             JC = 1
00202             DO 10 INFO = 1, N
00203                IF( AP( JC+INFO-1 ).EQ.ZERO )
00204      $            RETURN
00205                JC = JC + INFO
00206    10       CONTINUE
00207          ELSE
00208             JC = 1
00209             DO 20 INFO = 1, N
00210                IF( AP( JC ).EQ.ZERO )
00211      $            RETURN
00212                JC = JC + N - INFO + 1
00213    20       CONTINUE
00214          END IF
00215       END IF
00216       INFO = 0
00217 *
00218 *     Solve A * x = b  or  A**T * x = b.
00219 *
00220       DO 30 J = 1, NRHS
00221          CALL DTPSV( UPLO, TRANS, DIAG, N, AP, B( 1, J ), 1 )
00222    30 CONTINUE
00223 *
00224       RETURN
00225 *
00226 *     End of DTPTRS
00227 *
00228       END
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