dlarzt.f.html

来自「famous linear algebra library (LAPACK) p」· HTML 代码 · 共 209 行 · 第 1/2 页

</span><span class="comment">*</span><span class="comment">  The shape of the matrix V and the storage of the vectors which define
</span><span class="comment">*</span><span class="comment">  the H(i) is best illustrated by the following example with n = 5 and
</span><span class="comment">*</span><span class="comment">  k = 3. The elements equal to 1 are not stored; the corresponding
</span><span class="comment">*</span><span class="comment">  array elements are modified but restored on exit. The rest of the
</span><span class="comment">*</span><span class="comment">  array is not used.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  DIRECT = 'F' and STOREV = 'C':         DIRECT = 'F' and STOREV = 'R':
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">                                              ______V_____
</span><span class="comment">*</span><span class="comment">         ( v1 v2 v3 )                        /            \
</span><span class="comment">*</span><span class="comment">         ( v1 v2 v3 )                      ( v1 v1 v1 v1 v1 . . . . 1 )
</span><span class="comment">*</span><span class="comment">     V = ( v1 v2 v3 )                      ( v2 v2 v2 v2 v2 . . . 1   )
</span><span class="comment">*</span><span class="comment">         ( v1 v2 v3 )                      ( v3 v3 v3 v3 v3 . . 1     )
</span><span class="comment">*</span><span class="comment">         ( v1 v2 v3 )
</span><span class="comment">*</span><span class="comment">            .  .  .
</span><span class="comment">*</span><span class="comment">            .  .  .
</span><span class="comment">*</span><span class="comment">            1  .  .
</span><span class="comment">*</span><span class="comment">               1  .
</span><span class="comment">*</span><span class="comment">                  1
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  DIRECT = 'B' and STOREV = 'C':         DIRECT = 'B' and STOREV = 'R':
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">                                                        ______V_____
</span><span class="comment">*</span><span class="comment">            1                                          /            \
</span><span class="comment">*</span><span class="comment">            .  1                           ( 1 . . . . v1 v1 v1 v1 v1 )
</span><span class="comment">*</span><span class="comment">            .  .  1                        ( . 1 . . . v2 v2 v2 v2 v2 )
</span><span class="comment">*</span><span class="comment">            .  .  .                        ( . . 1 . . v3 v3 v3 v3 v3 )
</span><span class="comment">*</span><span class="comment">            .  .  .
</span><span class="comment">*</span><span class="comment">         ( v1 v2 v3 )
</span><span class="comment">*</span><span class="comment">         ( v1 v2 v3 )
</span><span class="comment">*</span><span class="comment">     V = ( v1 v2 v3 )
</span><span class="comment">*</span><span class="comment">         ( v1 v2 v3 )
</span><span class="comment">*</span><span class="comment">         ( v1 v2 v3 )
</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
      PARAMETER          ( ZERO = 0.0D+0 )
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Local Scalars ..
</span>      INTEGER            I, INFO, J
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. External Subroutines ..
</span>      EXTERNAL           DGEMV, DTRMV, <a name="XERBLA.131"></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">     .. External Functions ..
</span>      LOGICAL            <a name="LSAME.134"></a><a href="lsame.f.html#LSAME.1">LSAME</a>
      EXTERNAL           <a name="LSAME.135"></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">     .. Executable Statements ..
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Check for currently supported options
</span><span class="comment">*</span><span class="comment">
</span>      INFO = 0
      IF( .NOT.<a name="LSAME.142"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( DIRECT, <span class="string">'B'</span> ) ) THEN
         INFO = -1
      ELSE IF( .NOT.<a name="LSAME.144"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( STOREV, <span class="string">'R'</span> ) ) THEN
         INFO = -2
      END IF
      IF( INFO.NE.0 ) THEN
         CALL <a name="XERBLA.148"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>( <span class="string">'<a name="DLARZT.148"></a><a href="dlarzt.f.html#DLARZT.1">DLARZT</a>'</span>, -INFO )
         RETURN
      END IF
<span class="comment">*</span><span class="comment">
</span>      DO 20 I = K, 1, -1
         IF( TAU( I ).EQ.ZERO ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           H(i)  =  I
</span><span class="comment">*</span><span class="comment">
</span>            DO 10 J = I, K
               T( J, I ) = ZERO
   10       CONTINUE
         ELSE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           general case
</span><span class="comment">*</span><span class="comment">
</span>            IF( I.LT.K ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">              T(i+1:k,i) = - tau(i) * V(i+1:k,1:n) * V(i,1:n)'
</span><span class="comment">*</span><span class="comment">
</span>               CALL DGEMV( <span class="string">'No transpose'</span>, K-I, N, -TAU( I ),
     $                     V( I+1, 1 ), LDV, V( I, 1 ), LDV, ZERO,
     $                     T( I+1, I ), 1 )
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">              T(i+1:k,i) = T(i+1:k,i+1:k) * T(i+1:k,i)
</span><span class="comment">*</span><span class="comment">
</span>               CALL DTRMV( <span class="string">'Lower'</span>, <span class="string">'No transpose'</span>, <span class="string">'Non-unit'</span>, K-I,
     $                     T( I+1, I+1 ), LDT, T( I+1, I ), 1 )
            END IF
            T( I, I ) = TAU( I )
         END IF
   20 CONTINUE
      RETURN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     End of <a name="DLARZT.182"></a><a href="dlarzt.f.html#DLARZT.1">DLARZT</a>
</span><span class="comment">*</span><span class="comment">
</span>      END

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