slarrj.f.html

来自「famous linear algebra library (LAPACK) p」· HTML 代码 · 共 303 行 · 第 1/2 页

         RIGHT = W( II ) + WERR( II )
         WIDTH = RIGHT - MID
         TMP = MAX( ABS( LEFT ), ABS( RIGHT ) )

<span class="comment">*</span><span class="comment">        The following test prevents the test of converged intervals
</span>         IF( WIDTH.LT.RTOL*TMP ) THEN
<span class="comment">*</span><span class="comment">           This interval has already converged and does not need refinement.
</span><span class="comment">*</span><span class="comment">           (Note that the gaps might change through refining the
</span><span class="comment">*</span><span class="comment">            eigenvalues, however, they can only get bigger.)
</span><span class="comment">*</span><span class="comment">           Remove it from the list.
</span>            IWORK( K-1 ) = -1
<span class="comment">*</span><span class="comment">           Make sure that I1 always points to the first unconverged interval
</span>            IF((I.EQ.I1).AND.(I.LT.I2)) I1 = I + 1
            IF((PREV.GE.I1).AND.(I.LE.I2)) IWORK( 2*PREV-1 ) = I + 1
         ELSE
<span class="comment">*</span><span class="comment">           unconverged interval found
</span>            PREV = I
<span class="comment">*</span><span class="comment">           Make sure that [LEFT,RIGHT] contains the desired eigenvalue
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Do while( CNT(LEFT).GT.I-1 )
</span><span class="comment">*</span><span class="comment">
</span>            FAC = ONE
 20         CONTINUE
            CNT = 0
            S = LEFT
            DPLUS = D( 1 ) - S
            IF( DPLUS.LT.ZERO ) CNT = CNT + 1
            DO 30 J = 2, N
               DPLUS = D( J ) - S - E2( J-1 )/DPLUS
               IF( DPLUS.LT.ZERO ) CNT = CNT + 1
 30         CONTINUE
            IF( CNT.GT.I-1 ) THEN
               LEFT = LEFT - WERR( II )*FAC
               FAC = TWO*FAC
               GO TO 20
            END IF
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Do while( CNT(RIGHT).LT.I )
</span><span class="comment">*</span><span class="comment">
</span>            FAC = ONE
 50         CONTINUE
            CNT = 0
            S = RIGHT
            DPLUS = D( 1 ) - S
            IF( DPLUS.LT.ZERO ) CNT = CNT + 1
            DO 60 J = 2, N
               DPLUS = D( J ) - S - E2( J-1 )/DPLUS
               IF( DPLUS.LT.ZERO ) CNT = CNT + 1
 60         CONTINUE
            IF( CNT.LT.I ) THEN
               RIGHT = RIGHT + WERR( II )*FAC
               FAC = TWO*FAC
               GO TO 50
            END IF
            NINT = NINT + 1
            IWORK( K-1 ) = I + 1
            IWORK( K ) = CNT
         END IF
         WORK( K-1 ) = LEFT
         WORK( K ) = RIGHT
 75   CONTINUE


      SAVI1 = I1
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Do while( NINT.GT.0 ), i.e. there are still unconverged intervals
</span><span class="comment">*</span><span class="comment">     and while (ITER.LT.MAXITR)
</span><span class="comment">*</span><span class="comment">
</span>      ITER = 0
 80   CONTINUE
      PREV = I1 - 1
      I = I1
      OLNINT = NINT

      DO 100 P = 1, OLNINT
         K = 2*I
         II = I - OFFSET
         NEXT = IWORK( K-1 )
         LEFT = WORK( K-1 )
         RIGHT = WORK( K )
         MID = HALF*( LEFT + RIGHT )

<span class="comment">*</span><span class="comment">        semiwidth of interval
</span>         WIDTH = RIGHT - MID
         TMP = MAX( ABS( LEFT ), ABS( RIGHT ) )

         IF( ( WIDTH.LT.RTOL*TMP ) .OR.
     $      (ITER.EQ.MAXITR) )THEN
<span class="comment">*</span><span class="comment">           reduce number of unconverged intervals
</span>            NINT = NINT - 1
<span class="comment">*</span><span class="comment">           Mark interval as converged.
</span>            IWORK( K-1 ) = 0
            IF( I1.EQ.I ) THEN
               I1 = NEXT
            ELSE
<span class="comment">*</span><span class="comment">              Prev holds the last unconverged interval previously examined
</span>               IF(PREV.GE.I1) IWORK( 2*PREV-1 ) = NEXT
            END IF
            I = NEXT
            GO TO 100
         END IF
         PREV = I
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Perform one bisection step
</span><span class="comment">*</span><span class="comment">
</span>         CNT = 0
         S = MID
         DPLUS = D( 1 ) - S
         IF( DPLUS.LT.ZERO ) CNT = CNT + 1
         DO 90 J = 2, N
            DPLUS = D( J ) - S - E2( J-1 )/DPLUS
            IF( DPLUS.LT.ZERO ) CNT = CNT + 1
 90      CONTINUE
         IF( CNT.LE.I-1 ) THEN
            WORK( K-1 ) = MID
         ELSE
            WORK( K ) = MID
         END IF
         I = NEXT

 100  CONTINUE
      ITER = ITER + 1
<span class="comment">*</span><span class="comment">     do another loop if there are still unconverged intervals
</span><span class="comment">*</span><span class="comment">     However, in the last iteration, all intervals are accepted
</span><span class="comment">*</span><span class="comment">     since this is the best we can do.
</span>      IF( ( NINT.GT.0 ).AND.(ITER.LE.MAXITR) ) GO TO 80
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     At this point, all the intervals have converged
</span>      DO 110 I = SAVI1, ILAST
         K = 2*I
         II = I - OFFSET
<span class="comment">*</span><span class="comment">        All intervals marked by '0' have been refined.
</span>         IF( IWORK( K-1 ).EQ.0 ) THEN
            W( II ) = HALF*( WORK( K-1 )+WORK( K ) )
            WERR( II ) = WORK( K ) - W( II )
         END IF
 110  CONTINUE
<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="SLARRJ.278"></a><a href="slarrj.f.html#SLARRJ.1">SLARRJ</a>
</span><span class="comment">*</span><span class="comment">
</span>      END

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