dlasq4.f.html

来自「famous linear algebra library (LAPACK) p」· HTML 代码 · 共 352 行 · 第 1/2 页

</span>               A2 = A2 + B2
               DO 10 I4 = NP, 4*I0 - 1 + PP, -4
                  IF( B2.EQ.ZERO )
     $               GO TO 20
                  B1 = B2
                  IF( Z( I4 ) .GT. Z( I4-2 ) )
     $               RETURN
                  B2 = B2*( Z( I4 ) / Z( I4-2 ) )
                  A2 = A2 + B2
                  IF( HUNDRD*MAX( B2, B1 ).LT.A2 .OR. CNST1.LT.A2 ) 
     $               GO TO 20
   10          CONTINUE
   20          CONTINUE
               A2 = CNST3*A2
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">              Rayleigh quotient residual bound.
</span><span class="comment">*</span><span class="comment">
</span>               IF( A2.LT.CNST1 )
     $            S = GAM*( ONE-SQRT( A2 ) ) / ( ONE+A2 )
            END IF
         ELSE IF( DMIN.EQ.DN2 ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Case 5.
</span><span class="comment">*</span><span class="comment">
</span>            TTYPE = -5
            S = QURTR*DMIN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Compute contribution to norm squared from I &gt; NN-2.
</span><span class="comment">*</span><span class="comment">
</span>            NP = NN - 2*PP
            B1 = Z( NP-2 )
            B2 = Z( NP-6 )
            GAM = DN2
            IF( Z( NP-8 ).GT.B2 .OR. Z( NP-4 ).GT.B1 )
     $         RETURN
            A2 = ( Z( NP-8 ) / B2 )*( ONE+Z( NP-4 ) / B1 )
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Approximate contribution to norm squared from I &lt; NN-2.
</span><span class="comment">*</span><span class="comment">
</span>            IF( N0-I0.GT.2 ) THEN
               B2 = Z( NN-13 ) / Z( NN-15 )
               A2 = A2 + B2
               DO 30 I4 = NN - 17, 4*I0 - 1 + PP, -4
                  IF( B2.EQ.ZERO )
     $               GO TO 40
                  B1 = B2
                  IF( Z( I4 ) .GT. Z( I4-2 ) )
     $               RETURN
                  B2 = B2*( Z( I4 ) / Z( I4-2 ) )
                  A2 = A2 + B2
                  IF( HUNDRD*MAX( B2, B1 ).LT.A2 .OR. CNST1.LT.A2 ) 
     $               GO TO 40
   30          CONTINUE
   40          CONTINUE
               A2 = CNST3*A2
            END IF
<span class="comment">*</span><span class="comment">
</span>            IF( A2.LT.CNST1 )
     $         S = GAM*( ONE-SQRT( A2 ) ) / ( ONE+A2 )
         ELSE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Case 6, no information to guide us.
</span><span class="comment">*</span><span class="comment">
</span>            IF( TTYPE.EQ.-6 ) THEN
               G = G + THIRD*( ONE-G )
            ELSE IF( TTYPE.EQ.-18 ) THEN
               G = QURTR*THIRD
            ELSE
               G = QURTR
            END IF
            S = G*DMIN
            TTYPE = -6
         END IF
<span class="comment">*</span><span class="comment">
</span>      ELSE IF( N0IN.EQ.( N0+1 ) ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        One eigenvalue just deflated. Use DMIN1, DN1 for DMIN and DN.
</span><span class="comment">*</span><span class="comment">
</span>         IF( DMIN1.EQ.DN1 .AND. DMIN2.EQ.DN2 ) THEN 
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Cases 7 and 8.
</span><span class="comment">*</span><span class="comment">
</span>            TTYPE = -7
            S = THIRD*DMIN1
            IF( Z( NN-5 ).GT.Z( NN-7 ) )
     $         RETURN
            B1 = Z( NN-5 ) / Z( NN-7 )
            B2 = B1
            IF( B2.EQ.ZERO )
     $         GO TO 60
            DO 50 I4 = 4*N0 - 9 + PP, 4*I0 - 1 + PP, -4
               A2 = B1
               IF( Z( I4 ).GT.Z( I4-2 ) )
     $            RETURN
               B1 = B1*( Z( I4 ) / Z( I4-2 ) )
               B2 = B2 + B1
               IF( HUNDRD*MAX( B1, A2 ).LT.B2 ) 
     $            GO TO 60
   50       CONTINUE
   60       CONTINUE
            B2 = SQRT( CNST3*B2 )
            A2 = DMIN1 / ( ONE+B2**2 )
            GAP2 = HALF*DMIN2 - A2
            IF( GAP2.GT.ZERO .AND. GAP2.GT.B2*A2 ) THEN
               S = MAX( S, A2*( ONE-CNST2*A2*( B2 / GAP2 )*B2 ) )
            ELSE 
               S = MAX( S, A2*( ONE-CNST2*B2 ) )
               TTYPE = -8
            END IF
         ELSE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Case 9.
</span><span class="comment">*</span><span class="comment">
</span>            S = QURTR*DMIN1
            IF( DMIN1.EQ.DN1 )
     $         S = HALF*DMIN1
            TTYPE = -9
         END IF
<span class="comment">*</span><span class="comment">
</span>      ELSE IF( N0IN.EQ.( N0+2 ) ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Two eigenvalues deflated. Use DMIN2, DN2 for DMIN and DN.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Cases 10 and 11.
</span><span class="comment">*</span><span class="comment">
</span>         IF( DMIN2.EQ.DN2 .AND. TWO*Z( NN-5 ).LT.Z( NN-7 ) ) THEN 
            TTYPE = -10
            S = THIRD*DMIN2
            IF( Z( NN-5 ).GT.Z( NN-7 ) )
     $         RETURN
            B1 = Z( NN-5 ) / Z( NN-7 )
            B2 = B1
            IF( B2.EQ.ZERO )
     $         GO TO 80
            DO 70 I4 = 4*N0 - 9 + PP, 4*I0 - 1 + PP, -4
               IF( Z( I4 ).GT.Z( I4-2 ) )
     $            RETURN
               B1 = B1*( Z( I4 ) / Z( I4-2 ) )
               B2 = B2 + B1
               IF( HUNDRD*B1.LT.B2 )
     $            GO TO 80
   70       CONTINUE
   80       CONTINUE
            B2 = SQRT( CNST3*B2 )
            A2 = DMIN2 / ( ONE+B2**2 )
            GAP2 = Z( NN-7 ) + Z( NN-9 ) -
     $             SQRT( Z( NN-11 ) )*SQRT( Z( NN-9 ) ) - A2
            IF( GAP2.GT.ZERO .AND. GAP2.GT.B2*A2 ) THEN
               S = MAX( S, A2*( ONE-CNST2*A2*( B2 / GAP2 )*B2 ) )
            ELSE 
               S = MAX( S, A2*( ONE-CNST2*B2 ) )
            END IF
         ELSE
            S = QURTR*DMIN2
            TTYPE = -11
         END IF
      ELSE IF( N0IN.GT.( N0+2 ) ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Case 12, more than two eigenvalues deflated. No information.
</span><span class="comment">*</span><span class="comment">
</span>         S = ZERO 
         TTYPE = -12
      END IF
<span class="comment">*</span><span class="comment">
</span>      TAU = S
      RETURN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     End of <a name="DLASQ4.327"></a><a href="dlasq4.f.html#DLASQ4.1">DLASQ4</a>
</span><span class="comment">*</span><span class="comment">
</span>      END

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