slasq3.f.html

来自「famous linear algebra library (LAPACK) p」· HTML 代码 · 共 320 行 · 第 1/2 页

         S = Z( NN-3 )
         Z( NN-3 ) = Z( NN-7 )
         Z( NN-7 ) = S
      END IF
      IF( Z( NN-5 ).GT.Z( NN-3 )*TOL2 ) THEN
         T = HALF*( ( Z( NN-7 )-Z( NN-3 ) )+Z( NN-5 ) )
         S = Z( NN-3 )*( Z( NN-5 ) / T )
         IF( S.LE.T ) THEN
            S = Z( NN-3 )*( Z( NN-5 ) /
     $          ( T*( ONE+SQRT( ONE+S / T ) ) ) )
         ELSE
            S = Z( NN-3 )*( Z( NN-5 ) / ( T+SQRT( T )*SQRT( T+S ) ) )
         END IF
         T = Z( NN-7 ) + ( S+Z( NN-5 ) )
         Z( NN-3 ) = Z( NN-3 )*( Z( NN-7 ) / T )
         Z( NN-7 ) = T
      END IF
      Z( 4*N0-7 ) = Z( NN-7 ) + SIGMA
      Z( 4*N0-3 ) = Z( NN-3 ) + SIGMA
      N0 = N0 - 2
      GO TO 10
<span class="comment">*</span><span class="comment">
</span>   50 CONTINUE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Reverse the qd-array, if warranted.
</span><span class="comment">*</span><span class="comment">
</span>      IF( DMIN.LE.ZERO .OR. N0.LT.N0IN ) THEN
         IF( CBIAS*Z( 4*I0+PP-3 ).LT.Z( 4*N0+PP-3 ) ) THEN
            IPN4 = 4*( I0+N0 )
            DO 60 J4 = 4*I0, 2*( I0+N0-1 ), 4
               TEMP = Z( J4-3 )
               Z( J4-3 ) = Z( IPN4-J4-3 )
               Z( IPN4-J4-3 ) = TEMP
               TEMP = Z( J4-2 )
               Z( J4-2 ) = Z( IPN4-J4-2 )
               Z( IPN4-J4-2 ) = TEMP
               TEMP = Z( J4-1 )
               Z( J4-1 ) = Z( IPN4-J4-5 )
               Z( IPN4-J4-5 ) = TEMP
               TEMP = Z( J4 )
               Z( J4 ) = Z( IPN4-J4-4 )
               Z( IPN4-J4-4 ) = TEMP
   60       CONTINUE
            IF( N0-I0.LE.4 ) THEN
               Z( 4*N0+PP-1 ) = Z( 4*I0+PP-1 )
               Z( 4*N0-PP ) = Z( 4*I0-PP )
            END IF
            DMIN2 = MIN( DMIN2, Z( 4*N0+PP-1 ) )
            Z( 4*N0+PP-1 ) = MIN( Z( 4*N0+PP-1 ), Z( 4*I0+PP-1 ),
     $                            Z( 4*I0+PP+3 ) )
            Z( 4*N0-PP ) = MIN( Z( 4*N0-PP ), Z( 4*I0-PP ),
     $                          Z( 4*I0-PP+4 ) )
            QMAX = MAX( QMAX, Z( 4*I0+PP-3 ), Z( 4*I0+PP+1 ) )
            DMIN = -ZERO
         END IF
      END IF
<span class="comment">*</span><span class="comment">
</span>      IF( DMIN.LT.ZERO .OR. SAFMIN*QMAX.LT.MIN( Z( 4*N0+PP-1 ),
     $    Z( 4*N0+PP-9 ), DMIN2+Z( 4*N0-PP ) ) ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Choose a shift.
</span><span class="comment">*</span><span class="comment">
</span>         CALL <a name="SLASQ4.204"></a><a href="slasq4.f.html#SLASQ4.1">SLASQ4</a>( I0, N0, Z, PP, N0IN, DMIN, DMIN1, DMIN2, DN, DN1,
     $                DN2, TAU, TTYPE )
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Call dqds until DMIN &gt; 0.
</span><span class="comment">*</span><span class="comment">
</span>   80    CONTINUE
<span class="comment">*</span><span class="comment">
</span>         CALL <a name="SLASQ5.211"></a><a href="slasq5.f.html#SLASQ5.1">SLASQ5</a>( I0, N0, Z, PP, TAU, DMIN, DMIN1, DMIN2, DN,
     $                DN1, DN2, IEEE )
<span class="comment">*</span><span class="comment">
</span>         NDIV = NDIV + ( N0-I0+2 )
         ITER = ITER + 1
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Check status.
</span><span class="comment">*</span><span class="comment">
</span>         IF( DMIN.GE.ZERO .AND. DMIN1.GT.ZERO ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Success.
</span><span class="comment">*</span><span class="comment">
</span>            GO TO 100
<span class="comment">*</span><span class="comment">
</span>         ELSE IF( DMIN.LT.ZERO .AND. DMIN1.GT.ZERO .AND.
     $            Z( 4*( N0-1 )-PP ).LT.TOL*( SIGMA+DN1 ) .AND.
     $            ABS( DN ).LT.TOL*SIGMA ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Convergence hidden by negative DN.
</span><span class="comment">*</span><span class="comment">
</span>            Z( 4*( N0-1 )-PP+2 ) = ZERO
            DMIN = ZERO
            GO TO 100
         ELSE IF( DMIN.LT.ZERO ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           TAU too big. Select new TAU and try again.
</span><span class="comment">*</span><span class="comment">
</span>            NFAIL = NFAIL + 1
            IF( TTYPE.LT.-22 ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">              Failed twice. Play it safe.
</span><span class="comment">*</span><span class="comment">
</span>               TAU = ZERO
            ELSE IF( DMIN1.GT.ZERO ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">              Late failure. Gives excellent shift.
</span><span class="comment">*</span><span class="comment">
</span>               TAU = ( TAU+DMIN )*( ONE-TWO*EPS )
               TTYPE = TTYPE - 11
            ELSE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">              Early failure. Divide by 4.
</span><span class="comment">*</span><span class="comment">
</span>               TAU = QURTR*TAU
               TTYPE = TTYPE - 12
            END IF
            GO TO 80
         ELSE IF( DMIN.NE.DMIN ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           NaN.
</span><span class="comment">*</span><span class="comment">
</span>            TAU = ZERO
            GO TO 80
         ELSE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Possible underflow. Play it safe.
</span><span class="comment">*</span><span class="comment">
</span>            GO TO 90
         END IF
      END IF
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Risk of underflow.
</span><span class="comment">*</span><span class="comment">
</span>   90 CONTINUE
      CALL <a name="SLASQ6.275"></a><a href="slasq6.f.html#SLASQ6.1">SLASQ6</a>( I0, N0, Z, PP, DMIN, DMIN1, DMIN2, DN, DN1, DN2 )
      NDIV = NDIV + ( N0-I0+2 )
      ITER = ITER + 1
      TAU = ZERO
<span class="comment">*</span><span class="comment">
</span>  100 CONTINUE
      IF( TAU.LT.SIGMA ) THEN
         DESIG = DESIG + TAU
         T = SIGMA + DESIG
         DESIG = DESIG - ( T-SIGMA )
      ELSE
         T = SIGMA + TAU
         DESIG = SIGMA - ( T-TAU ) + DESIG
      END IF
      SIGMA = T
<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="SLASQ3.293"></a><a href="slasq3.f.html#SLASQ3.1">SLASQ3</a>
</span><span class="comment">*</span><span class="comment">
</span>      END

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