Return to dtptrs.f CVS log

Up to [local] / rpl / lapack / lapack

Première mise à jour de lapack et blas.

    1: *> \brief \b DTPTRS
    2: *
    3: *  =========== DOCUMENTATION ===========
    4: *
    5: * Online html documentation available at
    6: *            http://www.netlib.org/lapack/explore-html/
    7: *
    8: *> \htmlonly
    9: *> Download DTPTRS + dependencies
   10: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dtptrs.f">
   11: *> [TGZ]</a>
   12: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dtptrs.f">
   13: *> [ZIP]</a>
   14: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dtptrs.f">
   15: *> [TXT]</a>
   16: *> \endhtmlonly
   17: *
   18: *  Definition:
   19: *  ===========
   20: *
   21: *       SUBROUTINE DTPTRS( UPLO, TRANS, DIAG, N, NRHS, AP, B, LDB, INFO )
   22: *
   23: *       .. Scalar Arguments ..
   24: *       CHARACTER          DIAG, TRANS, UPLO
   25: *       INTEGER            INFO, LDB, N, NRHS
   26: *       ..
   27: *       .. Array Arguments ..
   28: *       DOUBLE PRECISION   AP( * ), B( LDB, * )
   29: *       ..
   30: *
   31: *
   32: *> \par Purpose:
   33: *  =============
   34: *>
   35: *> \verbatim
   36: *>
   37: *> DTPTRS solves a triangular system of the form
   38: *>
   39: *>    A * X = B  or  A**T * X = B,
   40: *>
   41: *> where A is a triangular matrix of order N stored in packed format,
   42: *> and B is an N-by-NRHS matrix.  A check is made to verify that A is
   43: *> nonsingular.
   44: *> \endverbatim
   45: *
   46: *  Arguments:
   47: *  ==========
   48: *
   49: *> \param[in] UPLO
   50: *> \verbatim
   51: *>          UPLO is CHARACTER*1
   52: *>          = 'U':  A is upper triangular;
   53: *>          = 'L':  A is lower triangular.
   54: *> \endverbatim
   55: *>
   56: *> \param[in] TRANS
   57: *> \verbatim
   58: *>          TRANS is CHARACTER*1
   59: *>          Specifies the form of the system of equations:
   60: *>          = 'N':  A * X = B  (No transpose)
   61: *>          = 'T':  A**T * X = B  (Transpose)
   62: *>          = 'C':  A**H * X = B  (Conjugate transpose = Transpose)
   63: *> \endverbatim
   64: *>
   65: *> \param[in] DIAG
   66: *> \verbatim
   67: *>          DIAG is CHARACTER*1
   68: *>          = 'N':  A is non-unit triangular;
   69: *>          = 'U':  A is unit triangular.
   70: *> \endverbatim
   71: *>
   72: *> \param[in] N
   73: *> \verbatim
   74: *>          N is INTEGER
   75: *>          The order of the matrix A.  N >= 0.
   76: *> \endverbatim
   77: *>
   78: *> \param[in] NRHS
   79: *> \verbatim
   80: *>          NRHS is INTEGER
   81: *>          The number of right hand sides, i.e., the number of columns
   82: *>          of the matrix B.  NRHS >= 0.
   83: *> \endverbatim
   84: *>
   85: *> \param[in] AP
   86: *> \verbatim
   87: *>          AP is DOUBLE PRECISION array, dimension (N*(N+1)/2)
   88: *>          The upper or lower triangular matrix A, packed columnwise in
   89: *>          a linear array.  The j-th column of A is stored in the array
   90: *>          AP as follows:
   91: *>          if UPLO = 'U', AP(i + (j-1)*j/2) = A(i,j) for 1<=i<=j;
   92: *>          if UPLO = 'L', AP(i + (j-1)*(2*n-j)/2) = A(i,j) for j<=i<=n.
   93: *> \endverbatim
   94: *>
   95: *> \param[in,out] B
   96: *> \verbatim
   97: *>          B is DOUBLE PRECISION array, dimension (LDB,NRHS)
   98: *>          On entry, the right hand side matrix B.
   99: *>          On exit, if INFO = 0, the solution matrix X.
  100: *> \endverbatim
  101: *>
  102: *> \param[in] LDB
  103: *> \verbatim
  104: *>          LDB is INTEGER
  105: *>          The leading dimension of the array B.  LDB >= max(1,N).
  106: *> \endverbatim
  107: *>
  108: *> \param[out] INFO
  109: *> \verbatim
  110: *>          INFO is INTEGER
  111: *>          = 0:  successful exit
  112: *>          < 0:  if INFO = -i, the i-th argument had an illegal value
  113: *>          > 0:  if INFO = i, the i-th diagonal element of A is zero,
  114: *>                indicating that the matrix is singular and the
  115: *>                solutions X have not been computed.
  116: *> \endverbatim
  117: *
  118: *  Authors:
  119: *  ========
  120: *
  121: *> \author Univ. of Tennessee
  122: *> \author Univ. of California Berkeley
  123: *> \author Univ. of Colorado Denver
  124: *> \author NAG Ltd.
  125: *
  126: *> \ingroup doubleOTHERcomputational
  127: *
  128: *  =====================================================================
  129:       SUBROUTINE DTPTRS( UPLO, TRANS, DIAG, N, NRHS, AP, B, LDB, INFO )
  130: *
  131: *  -- LAPACK computational routine --
  132: *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
  133: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
  134: *
  135: *     .. Scalar Arguments ..
  136:       CHARACTER          DIAG, TRANS, UPLO
  137:       INTEGER            INFO, LDB, N, NRHS
  138: *     ..
  139: *     .. Array Arguments ..
  140:       DOUBLE PRECISION   AP( * ), B( LDB, * )
  141: *     ..
  142: *
  143: *  =====================================================================
  144: *
  145: *     .. Parameters ..
  146:       DOUBLE PRECISION   ZERO
  147:       PARAMETER          ( ZERO = 0.0D+0 )
  148: *     ..
  149: *     .. Local Scalars ..
  150:       LOGICAL            NOUNIT, UPPER
  151:       INTEGER            J, JC
  152: *     ..
  153: *     .. External Functions ..
  154:       LOGICAL            LSAME
  155:       EXTERNAL           LSAME
  156: *     ..
  157: *     .. External Subroutines ..
  158:       EXTERNAL           DTPSV, XERBLA
  159: *     ..
  160: *     .. Intrinsic Functions ..
  161:       INTRINSIC          MAX
  162: *     ..
  163: *     .. Executable Statements ..
  164: *
  165: *     Test the input parameters.
  166: *
  167:       INFO = 0
  168:       UPPER = LSAME( UPLO, 'U' )
  169:       NOUNIT = LSAME( DIAG, 'N' )
  170:       IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
  171:          INFO = -1
  172:       ELSE IF( .NOT.LSAME( TRANS, 'N' ) .AND. .NOT.
  173:      $         LSAME( TRANS, 'T' ) .AND. .NOT.LSAME( TRANS, 'C' ) ) THEN
  174:          INFO = -2
  175:       ELSE IF( .NOT.NOUNIT .AND. .NOT.LSAME( DIAG, 'U' ) ) THEN
  176:          INFO = -3
  177:       ELSE IF( N.LT.0 ) THEN
  178:          INFO = -4
  179:       ELSE IF( NRHS.LT.0 ) THEN
  180:          INFO = -5
  181:       ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
  182:          INFO = -8
  183:       END IF
  184:       IF( INFO.NE.0 ) THEN
  185:          CALL XERBLA( 'DTPTRS', -INFO )
  186:          RETURN
  187:       END IF
  188: *
  189: *     Quick return if possible
  190: *
  191:       IF( N.EQ.0 )
  192:      $   RETURN
  193: *
  194: *     Check for singularity.
  195: *
  196:       IF( NOUNIT ) THEN
  197:          IF( UPPER ) THEN
  198:             JC = 1
  199:             DO 10 INFO = 1, N
  200:                IF( AP( JC+INFO-1 ).EQ.ZERO )
  201:      $            RETURN
  202:                JC = JC + INFO
  203:    10       CONTINUE
  204:          ELSE
  205:             JC = 1
  206:             DO 20 INFO = 1, N
  207:                IF( AP( JC ).EQ.ZERO )
  208:      $            RETURN
  209:                JC = JC + N - INFO + 1
  210:    20       CONTINUE
  211:          END IF
  212:       END IF
  213:       INFO = 0
  214: *
  215: *     Solve A * x = b  or  A**T * x = b.
  216: *
  217:       DO 30 J = 1, NRHS
  218:          CALL DTPSV( UPLO, TRANS, DIAG, N, AP, B( 1, J ), 1 )
  219:    30 CONTINUE
  220: *
  221:       RETURN
  222: *
  223: *     End of DTPTRS
  224: *
  225:       END