dopgtr.f.html

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      SUBROUTINE <a name="DOPGTR.1"></a><a href="dopgtr.f.html#DOPGTR.1">DOPGTR</a>( UPLO, N, AP, TAU, Q, LDQ, WORK, INFO )
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  -- LAPACK routine (version 3.1) --
</span><span class="comment">*</span><span class="comment">     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
</span><span class="comment">*</span><span class="comment">     November 2006
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     .. Scalar Arguments ..
</span>      CHARACTER          UPLO
      INTEGER            INFO, LDQ, N
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Array Arguments ..
</span>      DOUBLE PRECISION   AP( * ), Q( LDQ, * ), TAU( * ), WORK( * )
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Purpose
</span><span class="comment">*</span><span class="comment">  =======
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  <a name="DOPGTR.18"></a><a href="dopgtr.f.html#DOPGTR.1">DOPGTR</a> generates a real orthogonal matrix Q which is defined as the
</span><span class="comment">*</span><span class="comment">  product of n-1 elementary reflectors H(i) of order n, as returned by
</span><span class="comment">*</span><span class="comment">  <a name="DSPTRD.20"></a><a href="dsptrd.f.html#DSPTRD.1">DSPTRD</a> using packed storage:
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  if UPLO = 'U', Q = H(n-1) . . . H(2) H(1),
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  if UPLO = 'L', Q = H(1) H(2) . . . H(n-1).
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Arguments
</span><span class="comment">*</span><span class="comment">  =========
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  UPLO    (input) CHARACTER*1
</span><span class="comment">*</span><span class="comment">          = 'U': Upper triangular packed storage used in previous
</span><span class="comment">*</span><span class="comment">                 call to <a name="DSPTRD.31"></a><a href="dsptrd.f.html#DSPTRD.1">DSPTRD</a>;
</span><span class="comment">*</span><span class="comment">          = 'L': Lower triangular packed storage used in previous
</span><span class="comment">*</span><span class="comment">                 call to <a name="DSPTRD.33"></a><a href="dsptrd.f.html#DSPTRD.1">DSPTRD</a>.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  N       (input) INTEGER
</span><span class="comment">*</span><span class="comment">          The order of the matrix Q. N &gt;= 0.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  AP      (input) DOUBLE PRECISION array, dimension (N*(N+1)/2)
</span><span class="comment">*</span><span class="comment">          The vectors which define the elementary reflectors, as
</span><span class="comment">*</span><span class="comment">          returned by <a name="DSPTRD.40"></a><a href="dsptrd.f.html#DSPTRD.1">DSPTRD</a>.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  TAU     (input) DOUBLE PRECISION array, dimension (N-1)
</span><span class="comment">*</span><span class="comment">          TAU(i) must contain the scalar factor of the elementary
</span><span class="comment">*</span><span class="comment">          reflector H(i), as returned by <a name="DSPTRD.44"></a><a href="dsptrd.f.html#DSPTRD.1">DSPTRD</a>.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Q       (output) DOUBLE PRECISION array, dimension (LDQ,N)
</span><span class="comment">*</span><span class="comment">          The N-by-N orthogonal matrix Q.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  LDQ     (input) INTEGER
</span><span class="comment">*</span><span class="comment">          The leading dimension of the array Q. LDQ &gt;= max(1,N).
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  WORK    (workspace) DOUBLE PRECISION array, dimension (N-1)
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  INFO    (output) INTEGER
</span><span class="comment">*</span><span class="comment">          = 0:  successful exit
</span><span class="comment">*</span><span class="comment">          &lt; 0:  if INFO = -i, the i-th argument had an illegal value
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  =====================================================================
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     .. Parameters ..
</span>      DOUBLE PRECISION   ZERO, ONE
      PARAMETER          ( ZERO = 0.0D+0, ONE = 1.0D+0 )
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Local Scalars ..
</span>      LOGICAL            UPPER
      INTEGER            I, IINFO, IJ, J
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. External Functions ..
</span>      LOGICAL            <a name="LSAME.69"></a><a href="lsame.f.html#LSAME.1">LSAME</a>
      EXTERNAL           <a name="LSAME.70"></a><a href="lsame.f.html#LSAME.1">LSAME</a>
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. External Subroutines ..
</span>      EXTERNAL           <a name="DORG2L.73"></a><a href="dorg2l.f.html#DORG2L.1">DORG2L</a>, <a name="DORG2R.73"></a><a href="dorg2r.f.html#DORG2R.1">DORG2R</a>, <a name="XERBLA.73"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Intrinsic Functions ..
</span>      INTRINSIC          MAX
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Executable Statements ..
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Test the input arguments
</span><span class="comment">*</span><span class="comment">
</span>      INFO = 0
      UPPER = <a name="LSAME.83"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( UPLO, <span class="string">'U'</span> )
      IF( .NOT.UPPER .AND. .NOT.<a name="LSAME.84"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( UPLO, <span class="string">'L'</span> ) ) THEN
         INFO = -1
      ELSE IF( N.LT.0 ) THEN
         INFO = -2
      ELSE IF( LDQ.LT.MAX( 1, N ) ) THEN
         INFO = -6
      END IF
      IF( INFO.NE.0 ) THEN
         CALL <a name="XERBLA.92"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>( <span class="string">'<a name="DOPGTR.92"></a><a href="dopgtr.f.html#DOPGTR.1">DOPGTR</a>'</span>, -INFO )
         RETURN
      END IF
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Quick return if possible
</span><span class="comment">*</span><span class="comment">
</span>      IF( N.EQ.0 )
     $   RETURN
<span class="comment">*</span><span class="comment">
</span>      IF( UPPER ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Q was determined by a call to <a name="DSPTRD.103"></a><a href="dsptrd.f.html#DSPTRD.1">DSPTRD</a> with UPLO = 'U'
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Unpack the vectors which define the elementary reflectors and
</span><span class="comment">*</span><span class="comment">        set the last row and column of Q equal to those of the unit
</span><span class="comment">*</span><span class="comment">        matrix
</span><span class="comment">*</span><span class="comment">
</span>         IJ = 2
         DO 20 J = 1, N - 1
            DO 10 I = 1, J - 1
               Q( I, J ) = AP( IJ )
               IJ = IJ + 1
   10       CONTINUE
            IJ = IJ + 2
            Q( N, J ) = ZERO
   20    CONTINUE
         DO 30 I = 1, N - 1
            Q( I, N ) = ZERO
   30    CONTINUE
         Q( N, N ) = ONE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Generate Q(1:n-1,1:n-1)
</span><span class="comment">*</span><span class="comment">
</span>         CALL <a name="DORG2L.125"></a><a href="dorg2l.f.html#DORG2L.1">DORG2L</a>( N-1, N-1, N-1, Q, LDQ, TAU, WORK, IINFO )
<span class="comment">*</span><span class="comment">
</span>      ELSE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Q was determined by a call to <a name="DSPTRD.129"></a><a href="dsptrd.f.html#DSPTRD.1">DSPTRD</a> with UPLO = 'L'.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Unpack the vectors which define the elementary reflectors and
</span><span class="comment">*</span><span class="comment">        set the first row and column of Q equal to those of the unit
</span><span class="comment">*</span><span class="comment">        matrix
</span><span class="comment">*</span><span class="comment">
</span>         Q( 1, 1 ) = ONE
         DO 40 I = 2, N
            Q( I, 1 ) = ZERO
   40    CONTINUE
         IJ = 3
         DO 60 J = 2, N
            Q( 1, J ) = ZERO
            DO 50 I = J + 1, N
               Q( I, J ) = AP( IJ )
               IJ = IJ + 1
   50       CONTINUE
            IJ = IJ + 2
   60    CONTINUE
         IF( N.GT.1 ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Generate Q(2:n,2:n)
</span><span class="comment">*</span><span class="comment">
</span>            CALL <a name="DORG2R.152"></a><a href="dorg2r.f.html#DORG2R.1">DORG2R</a>( N-1, N-1, N-1, Q( 2, 2 ), LDQ, TAU, WORK,
     $                   IINFO )
         END IF
      END IF
      RETURN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     End of <a name="DOPGTR.158"></a><a href="dopgtr.f.html#DOPGTR.1">DOPGTR</a>
</span><span class="comment">*</span><span class="comment">
</span>      END

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