sgeqlf.f.html

来自「famous linear algebra library (LAPACK) p」· HTML 代码 · 共 238 行 · 第 1/2 页

      LQUERY = ( LWORK.EQ.-1 )
      IF( M.LT.0 ) THEN
         INFO = -1
      ELSE IF( N.LT.0 ) 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
         K = MIN( M, N )
         IF( K.EQ.0 ) THEN
            LWKOPT = 1
         ELSE
            NB = <a name="ILAENV.115"></a><a href="hfy-index.html#ILAENV">ILAENV</a>( 1, <span class="string">'<a name="SGEQLF.115"></a><a href="sgeqlf.f.html#SGEQLF.1">SGEQLF</a>'</span>, <span class="string">' '</span>, M, N, -1, -1 )
            LWKOPT = N*NB
         END IF
         WORK( 1 ) = LWKOPT
<span class="comment">*</span><span class="comment">
</span>         IF( LWORK.LT.MAX( 1, N ) .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.126"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>( <span class="string">'<a name="SGEQLF.126"></a><a href="sgeqlf.f.html#SGEQLF.1">SGEQLF</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( K.EQ.0 ) THEN
         RETURN
      END IF
<span class="comment">*</span><span class="comment">
</span>      NBMIN = 2
      NX = 1
      IWS = N
      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.145"></a><a href="hfy-index.html#ILAENV">ILAENV</a>( 3, <span class="string">'<a name="SGEQLF.145"></a><a href="sgeqlf.f.html#SGEQLF.1">SGEQLF</a>'</span>, <span class="string">' '</span>, M, N, -1, -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 = N
            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.158"></a><a href="hfy-index.html#ILAENV">ILAENV</a>( 2, <span class="string">'<a name="SGEQLF.158"></a><a href="sgeqlf.f.html#SGEQLF.1">SGEQLF</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.K .AND. NX.LT.K ) 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 columns are handled by the block method.
</span><span class="comment">*</span><span class="comment">
</span>         KI = ( ( K-NX-1 ) / NB )*NB
         KK = MIN( K, KI+NB )
<span class="comment">*</span><span class="comment">
</span>         DO 10 I = K - KK + KI + 1, K - KK + 1, -NB
            IB = MIN( K-I+1, NB )
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Compute the QL factorization of the current block
</span><span class="comment">*</span><span class="comment">           A(1:m-k+i+ib-1,n-k+i:n-k+i+ib-1)
</span><span class="comment">*</span><span class="comment">
</span>            CALL <a name="SGEQL2.178"></a><a href="sgeql2.f.html#SGEQL2.1">SGEQL2</a>( M-K+I+IB-1, IB, A( 1, N-K+I ), LDA, TAU( I ),
     $                   WORK, IINFO )
            IF( N-K+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="SLARFT.185"></a><a href="slarft.f.html#SLARFT.1">SLARFT</a>( <span class="string">'Backward'</span>, <span class="string">'Columnwise'</span>, M-K+I+IB-1, IB,
     $                      A( 1, N-K+I ), 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+ib-1,1:n-k+i-1) from the left
</span><span class="comment">*</span><span class="comment">
</span>               CALL <a name="SLARFB.190"></a><a href="slarfb.f.html#SLARFB.1">SLARFB</a>( <span class="string">'Left'</span>, <span class="string">'Transpose'</span>, <span class="string">'Backward'</span>,
     $                      <span class="string">'Columnwise'</span>, M-K+I+IB-1, N-K+I-1, IB,
     $                      A( 1, N-K+I ), LDA, WORK, LDWORK, A, LDA,
     $                      WORK( IB+1 ), LDWORK )
            END IF
   10    CONTINUE
         MU = M - K + I + NB - 1
         NU = N - K + I + NB - 1
      ELSE
         MU = M
         NU = N
      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 .AND. NU.GT.0 )
     $   CALL <a name="SGEQL2.206"></a><a href="sgeql2.f.html#SGEQL2.1">SGEQL2</a>( MU, NU, A, LDA, TAU, WORK, IINFO )
<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="SGEQLF.211"></a><a href="sgeqlf.f.html#SGEQLF.1">SGEQLF</a>
</span><span class="comment">*</span><span class="comment">
</span>      END

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