cungrq.f.html

来自「famous linear algebra library (LAPACK) p」· HTML 代码 · 共 248 行 · 第 1/2 页

</span>      IF( INFO.EQ.0 ) THEN
         IF( M.LE.0 ) THEN
            LWKOPT = 1
         ELSE
            NB = <a name="ILAENV.110"></a><a href="hfy-index.html#ILAENV">ILAENV</a>( 1, <span class="string">'<a name="CUNGRQ.110"></a><a href="cungrq.f.html#CUNGRQ.1">CUNGRQ</a>'</span>, <span class="string">' '</span>, M, N, K, -1 )
            LWKOPT = M*NB
         END IF
         WORK( 1 ) = LWKOPT
<span class="comment">*</span><span class="comment">
</span>         IF( LWORK.LT.MAX( 1, M ) .AND. .NOT.LQUERY ) THEN
            INFO = -8
         END IF
      END IF
<span class="comment">*</span><span class="comment">
</span>      IF( INFO.NE.0 ) THEN
         CALL <a name="XERBLA.121"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>( <span class="string">'<a name="CUNGRQ.121"></a><a href="cungrq.f.html#CUNGRQ.1">CUNGRQ</a>'</span>, -INFO )
         RETURN
      ELSE IF( LQUERY ) THEN
         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( M.LE.0 ) THEN
         RETURN
      END IF
<span class="comment">*</span><span class="comment">
</span>      NBMIN = 2
      NX = 0
      IWS = M
      IF( NB.GT.1 .AND. NB.LT.K ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Determine when to cross over from blocked to unblocked code.
</span><span class="comment">*</span><span class="comment">
</span>         NX = MAX( 0, <a name="ILAENV.140"></a><a href="hfy-index.html#ILAENV">ILAENV</a>( 3, <span class="string">'<a name="CUNGRQ.140"></a><a href="cungrq.f.html#CUNGRQ.1">CUNGRQ</a>'</span>, <span class="string">' '</span>, M, N, K, -1 ) )
         IF( NX.LT.K ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Determine if workspace is large enough for blocked code.
</span><span class="comment">*</span><span class="comment">
</span>            LDWORK = M
            IWS = LDWORK*NB
            IF( LWORK.LT.IWS ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">              Not enough workspace to use optimal NB:  reduce NB and
</span><span class="comment">*</span><span class="comment">              determine the minimum value of NB.
</span><span class="comment">*</span><span class="comment">
</span>               NB = LWORK / LDWORK
               NBMIN = MAX( 2, <a name="ILAENV.153"></a><a href="hfy-index.html#ILAENV">ILAENV</a>( 2, <span class="string">'<a name="CUNGRQ.153"></a><a href="cungrq.f.html#CUNGRQ.1">CUNGRQ</a>'</span>, <span class="string">' '</span>, M, N, K, -1 ) )
            END IF
         END IF
      END IF
<span class="comment">*</span><span class="comment">
</span>      IF( NB.GE.NBMIN .AND. NB.LT.K .AND. NX.LT.K ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Use blocked code after the first block.
</span><span class="comment">*</span><span class="comment">        The last kk rows are handled by the block method.
</span><span class="comment">*</span><span class="comment">
</span>         KK = MIN( K, ( ( K-NX+NB-1 ) / NB )*NB )
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Set A(1:m-kk,n-kk+1:n) to zero.
</span><span class="comment">*</span><span class="comment">
</span>         DO 20 J = N - KK + 1, N
            DO 10 I = 1, M - KK
               A( I, J ) = ZERO
   10       CONTINUE
   20    CONTINUE
      ELSE
         KK = 0
      END IF
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Use unblocked code for the first or only block.
</span><span class="comment">*</span><span class="comment">
</span>      CALL <a name="CUNGR2.178"></a><a href="cungr2.f.html#CUNGR2.1">CUNGR2</a>( M-KK, N-KK, K-KK, A, LDA, TAU, WORK, IINFO )
<span class="comment">*</span><span class="comment">
</span>      IF( KK.GT.0 ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Use blocked code
</span><span class="comment">*</span><span class="comment">
</span>         DO 50 I = K - KK + 1, K, NB
            IB = MIN( NB, K-I+1 )
            II = M - K + I
            IF( II.GT.1 ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">              Form the triangular factor of the block reflector
</span><span class="comment">*</span><span class="comment">              H = H(i+ib-1) . . . H(i+1) H(i)
</span><span class="comment">*</span><span class="comment">
</span>               CALL <a name="CLARFT.192"></a><a href="clarft.f.html#CLARFT.1">CLARFT</a>( <span class="string">'Backward'</span>, <span class="string">'Rowwise'</span>, N-K+I+IB-1, IB,
     $                      A( II, 1 ), LDA, TAU( I ), WORK, LDWORK )
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">              Apply H' to A(1:m-k+i-1,1:n-k+i+ib-1) from the right
</span><span class="comment">*</span><span class="comment">
</span>               CALL <a name="CLARFB.197"></a><a href="clarfb.f.html#CLARFB.1">CLARFB</a>( <span class="string">'Right'</span>, <span class="string">'Conjugate transpose'</span>, <span class="string">'Backward'</span>,
     $                      <span class="string">'Rowwise'</span>, II-1, N-K+I+IB-1, IB, A( II, 1 ),
     $                      LDA, WORK, LDWORK, A, LDA, WORK( IB+1 ),
     $                      LDWORK )
            END IF
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Apply H' to columns 1:n-k+i+ib-1 of current block
</span><span class="comment">*</span><span class="comment">
</span>            CALL <a name="CUNGR2.205"></a><a href="cungr2.f.html#CUNGR2.1">CUNGR2</a>( IB, N-K+I+IB-1, IB, A( II, 1 ), LDA, TAU( I ),
     $                   WORK, IINFO )
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Set columns n-k+i+ib:n of current block to zero
</span><span class="comment">*</span><span class="comment">
</span>            DO 40 L = N - K + I + IB, N
               DO 30 J = II, II + IB - 1
                  A( J, L ) = ZERO
   30          CONTINUE
   40       CONTINUE
   50    CONTINUE
      END IF
<span class="comment">*</span><span class="comment">
</span>      WORK( 1 ) = IWS
      RETURN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     End of <a name="CUNGRQ.221"></a><a href="cungrq.f.html#CUNGRQ.1">CUNGRQ</a>
</span><span class="comment">*</span><span class="comment">
</span>      END

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