dtzrzf.f.html

来自「famous linear algebra library (LAPACK) p」· HTML 代码 · 共 269 行 · 第 1/2 页

</span>      INTEGER            <a name="ILAENV.117"></a><a href="hfy-index.html#ILAENV">ILAENV</a>
      EXTERNAL           <a name="ILAENV.118"></a><a href="hfy-index.html#ILAENV">ILAENV</a>
<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
      LQUERY = ( LWORK.EQ.-1 )
      IF( M.LT.0 ) THEN
         INFO = -1
      ELSE IF( N.LT.M ) THEN
         INFO = -2
      ELSE IF( LDA.LT.MAX( 1, M ) ) THEN
         INFO = -4
      END IF
<span class="comment">*</span><span class="comment">
</span>      IF( INFO.EQ.0 ) THEN
         IF( M.EQ.0 .OR. M.EQ.N ) THEN
            LWKOPT = 1
         ELSE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Determine the block size.
</span><span class="comment">*</span><span class="comment">
</span>            NB = <a name="ILAENV.141"></a><a href="hfy-index.html#ILAENV">ILAENV</a>( 1, <span class="string">'<a name="DGERQF.141"></a><a href="dgerqf.f.html#DGERQF.1">DGERQF</a>'</span>, <span class="string">' '</span>, M, N, -1, -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 = -7
         END IF
      END IF
<span class="comment">*</span><span class="comment">
</span>      IF( INFO.NE.0 ) THEN
         CALL <a name="XERBLA.152"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>( <span class="string">'<a name="DTZRZF.152"></a><a href="dtzrzf.f.html#DTZRZF.1">DTZRZF</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.EQ.0 ) THEN
         RETURN
      ELSE IF( M.EQ.N ) THEN
         DO 10 I = 1, N
            TAU( I ) = ZERO
   10    CONTINUE
         RETURN
      END IF
<span class="comment">*</span><span class="comment">
</span>      NBMIN = 2
      NX = 1
      IWS = M
      IF( NB.GT.1 .AND. NB.LT.M ) 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.176"></a><a href="hfy-index.html#ILAENV">ILAENV</a>( 3, <span class="string">'<a name="DGERQF.176"></a><a href="dgerqf.f.html#DGERQF.1">DGERQF</a>'</span>, <span class="string">' '</span>, M, N, -1, -1 ) )
         IF( NX.LT.M ) 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.189"></a><a href="hfy-index.html#ILAENV">ILAENV</a>( 2, <span class="string">'<a name="DGERQF.189"></a><a href="dgerqf.f.html#DGERQF.1">DGERQF</a>'</span>, <span class="string">' '</span>, M, N, -1,
     $                 -1 ) )
            END IF
         END IF
      END IF
<span class="comment">*</span><span class="comment">
</span>      IF( NB.GE.NBMIN .AND. NB.LT.M .AND. NX.LT.M ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Use blocked code initially.
</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>         M1 = MIN( M+1, N )
         KI = ( ( M-NX-1 ) / NB )*NB
         KK = MIN( M, KI+NB )
<span class="comment">*</span><span class="comment">
</span>         DO 20 I = M - KK + KI + 1, M - KK + 1, -NB
            IB = MIN( M-I+1, NB )
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Compute the TZ factorization of the current block
</span><span class="comment">*</span><span class="comment">           A(i:i+ib-1,i:n)
</span><span class="comment">*</span><span class="comment">
</span>            CALL <a name="DLATRZ.210"></a><a href="dlatrz.f.html#DLATRZ.1">DLATRZ</a>( IB, N-I+1, N-M, A( I, I ), LDA, TAU( I ),
     $                   WORK )
            IF( I.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="DLARZT.217"></a><a href="dlarzt.f.html#DLARZT.1">DLARZT</a>( <span class="string">'Backward'</span>, <span class="string">'Rowwise'</span>, N-M, IB, A( I, M1 ),
     $                      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:i-1,i:n) from the right
</span><span class="comment">*</span><span class="comment">
</span>               CALL <a name="DLARZB.222"></a><a href="dlarzb.f.html#DLARZB.1">DLARZB</a>( <span class="string">'Right'</span>, <span class="string">'No transpose'</span>, <span class="string">'Backward'</span>,
     $                      <span class="string">'Rowwise'</span>, I-1, N-I+1, IB, N-M, A( I, M1 ),
     $                      LDA, WORK, LDWORK, A( 1, I ), LDA,
     $                      WORK( IB+1 ), LDWORK )
            END IF
   20    CONTINUE
         MU = I + NB - 1
      ELSE
         MU = M
      END IF
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Use unblocked code to factor the last or only block
</span><span class="comment">*</span><span class="comment">
</span>      IF( MU.GT.0 )
     $   CALL <a name="DLATRZ.236"></a><a href="dlatrz.f.html#DLATRZ.1">DLATRZ</a>( MU, N, N-M, A, LDA, TAU, WORK )
<span class="comment">*</span><span class="comment">
</span>      WORK( 1 ) = LWKOPT
<span class="comment">*</span><span class="comment">
</span>      RETURN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     End of <a name="DTZRZF.242"></a><a href="dtzrzf.f.html#DTZRZF.1">DTZRZF</a>
</span><span class="comment">*</span><span class="comment">
</span>      END

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