Return to dopgtr.f CVS log

Up to [local] / rpl / lapack / lapack

Mise à jour globale de Lapack 3.2.2.

    1:       SUBROUTINE DOPGTR( UPLO, N, AP, TAU, Q, LDQ, WORK, 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, LDQ, N
   11: *     ..
   12: *     .. Array Arguments ..
   13:       DOUBLE PRECISION   AP( * ), Q( LDQ, * ), TAU( * ), WORK( * )
   14: *     ..
   15: *
   16: *  Purpose
   17: *  =======
   18: *
   19: *  DOPGTR generates a real orthogonal matrix Q which is defined as the
   20: *  product of n-1 elementary reflectors H(i) of order n, as returned by
   21: *  DSPTRD using packed storage:
   22: *
   23: *  if UPLO = 'U', Q = H(n-1) . . . H(2) H(1),
   24: *
   25: *  if UPLO = 'L', Q = H(1) H(2) . . . H(n-1).
   26: *
   27: *  Arguments
   28: *  =========
   29: *
   30: *  UPLO    (input) CHARACTER*1
   31: *          = 'U': Upper triangular packed storage used in previous
   32: *                 call to DSPTRD;
   33: *          = 'L': Lower triangular packed storage used in previous
   34: *                 call to DSPTRD.
   35: *
   36: *  N       (input) INTEGER
   37: *          The order of the matrix Q. N >= 0.
   38: *
   39: *  AP      (input) DOUBLE PRECISION array, dimension (N*(N+1)/2)
   40: *          The vectors which define the elementary reflectors, as
   41: *          returned by DSPTRD.
   42: *
   43: *  TAU     (input) DOUBLE PRECISION array, dimension (N-1)
   44: *          TAU(i) must contain the scalar factor of the elementary
   45: *          reflector H(i), as returned by DSPTRD.
   46: *
   47: *  Q       (output) DOUBLE PRECISION array, dimension (LDQ,N)
   48: *          The N-by-N orthogonal matrix Q.
   49: *
   50: *  LDQ     (input) INTEGER
   51: *          The leading dimension of the array Q. LDQ >= max(1,N).
   52: *
   53: *  WORK    (workspace) DOUBLE PRECISION array, dimension (N-1)
   54: *
   55: *  INFO    (output) INTEGER
   56: *          = 0:  successful exit
   57: *          < 0:  if INFO = -i, the i-th argument had an illegal value
   58: *
   59: *  =====================================================================
   60: *
   61: *     .. Parameters ..
   62:       DOUBLE PRECISION   ZERO, ONE
   63:       PARAMETER          ( ZERO = 0.0D+0, ONE = 1.0D+0 )
   64: *     ..
   65: *     .. Local Scalars ..
   66:       LOGICAL            UPPER
   67:       INTEGER            I, IINFO, IJ, J
   68: *     ..
   69: *     .. External Functions ..
   70:       LOGICAL            LSAME
   71:       EXTERNAL           LSAME
   72: *     ..
   73: *     .. External Subroutines ..
   74:       EXTERNAL           DORG2L, DORG2R, XERBLA
   75: *     ..
   76: *     .. Intrinsic Functions ..
   77:       INTRINSIC          MAX
   78: *     ..
   79: *     .. Executable Statements ..
   80: *
   81: *     Test the input arguments
   82: *
   83:       INFO = 0
   84:       UPPER = LSAME( UPLO, 'U' )
   85:       IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
   86:          INFO = -1
   87:       ELSE IF( N.LT.0 ) THEN
   88:          INFO = -2
   89:       ELSE IF( LDQ.LT.MAX( 1, N ) ) THEN
   90:          INFO = -6
   91:       END IF
   92:       IF( INFO.NE.0 ) THEN
   93:          CALL XERBLA( 'DOPGTR', -INFO )
   94:          RETURN
   95:       END IF
   96: *
   97: *     Quick return if possible
   98: *
   99:       IF( N.EQ.0 )
  100:      $   RETURN
  101: *
  102:       IF( UPPER ) THEN
  103: *
  104: *        Q was determined by a call to DSPTRD with UPLO = 'U'
  105: *
  106: *        Unpack the vectors which define the elementary reflectors and
  107: *        set the last row and column of Q equal to those of the unit
  108: *        matrix
  109: *
  110:          IJ = 2
  111:          DO 20 J = 1, N - 1
  112:             DO 10 I = 1, J - 1
  113:                Q( I, J ) = AP( IJ )
  114:                IJ = IJ + 1
  115:    10       CONTINUE
  116:             IJ = IJ + 2
  117:             Q( N, J ) = ZERO
  118:    20    CONTINUE
  119:          DO 30 I = 1, N - 1
  120:             Q( I, N ) = ZERO
  121:    30    CONTINUE
  122:          Q( N, N ) = ONE
  123: *
  124: *        Generate Q(1:n-1,1:n-1)
  125: *
  126:          CALL DORG2L( N-1, N-1, N-1, Q, LDQ, TAU, WORK, IINFO )
  127: *
  128:       ELSE
  129: *
  130: *        Q was determined by a call to DSPTRD with UPLO = 'L'.
  131: *
  132: *        Unpack the vectors which define the elementary reflectors and
  133: *        set the first row and column of Q equal to those of the unit
  134: *        matrix
  135: *
  136:          Q( 1, 1 ) = ONE
  137:          DO 40 I = 2, N
  138:             Q( I, 1 ) = ZERO
  139:    40    CONTINUE
  140:          IJ = 3
  141:          DO 60 J = 2, N
  142:             Q( 1, J ) = ZERO
  143:             DO 50 I = J + 1, N
  144:                Q( I, J ) = AP( IJ )
  145:                IJ = IJ + 1
  146:    50       CONTINUE
  147:             IJ = IJ + 2
  148:    60    CONTINUE
  149:          IF( N.GT.1 ) THEN
  150: *
  151: *           Generate Q(2:n,2:n)
  152: *
  153:             CALL DORG2R( N-1, N-1, N-1, Q( 2, 2 ), LDQ, TAU, WORK,
  154:      $                   IINFO )
  155:          END IF
  156:       END IF
  157:       RETURN
  158: *
  159: *     End of DOPGTR
  160: *
  161:       END