$BJd@52aDx(B

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$\begin{figure}\begin{center} \Depsf[80mm][]{ps-fig/fig2.ps} \end{center} \end{figure}$

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$B$N>l9g$K$b(B

$\begin{displaymath} \rho _{i}^{n+1} = \rho _{i}^{n} + \frac{1}{8}(\rho _{i+1}^{n}-2\rho _{i}^{n} +\rho _{i-1}^{n}), \end{displaymath}$

(6')

$B$H$J$C$F3H;6$,;D$C$F$7$^$&(B. $B$3$l$r=|$$$?=$@52r(B $\overline{\rho }_ {i}^{n+1}$ $B$r5a$a$k$?$a$K(B, (6)$B<0$rM[2rK!$G5U$K2r$/(B.

$\begin{displaymath} \overline{\rho }_{i}^{n+1} = \rho _{i}^{n+1} - \frac{1}{8}(\rho _{i+1}^{n+1}-2\rho _{i}^{n+1} +\rho _{i-1}^{n+1}), \end{displaymath}$

(7')

(7)$B<01&JUBhFs9`$r(B ``antidiffusion'' $B$H8F$V(B. (

)$B$O7A<0E*$K0\N.7A$K$9$k$3$H$,$G$-$k(B. $B$9$J$o$A(B,

$\displaystyle \overline{\rho }_{i}^{n+1}$	$\textstyle =$	$\displaystyle \rho _{i}^{n+1} - (f_{i+\frac{1}{2}} - f_{i-\frac{1}{2}}),$	(8')
$\displaystyle f_{i\pm \frac{1}{2}}$	$\textstyle \equiv$	$\displaystyle \pm \frac{1}{8}(\rho _{i\pm 1}^{n+1}-\rho _{i}^{n+1}),$	(9')

$B$H$J$k(B. $f_{i\pm \frac{1}{2}}$ $B$O(B antidiffusive $B%U%i%C%/%9(B $B$H8F$V(B.

$B$3$N(B antidiffusion $B$^$?$O(B antidiffusive $B%U%i%C%/%9$r2C$($l$P?tCM3H;6(B $B$r=|5n$9$k$3$H$,$G$-$k$N$G(B,$B$$$D$G$b@5$7$$2r$,F@$i$l$k$+$H$$$&$H2$B$N$h$&$JITO"B3LL$,0lDj$NB.EY(B $B$G0\N.$5$l$k$h$&$J>l9g$r9M$($F$_$h$&(B. $B$"$k;~9o$G?^$N$h$&$K@5$7$$2r(B $B$,F@$i$l$F$$$k$H$9$k(B. $B$3$l$K(B antidiffusion $B$r2C$($k$H?^$K<($7$?Lp(B $B0u$N$h$&$K(B

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$B$KIi$NCM$,@8$8$F$7$^$&(B. $BL@$i$+$K$3$l$OHsJ*M}E*$J2r$G$"(B $B$k(B.

antidiffusion $B$r2C$($k$H$-$O0J>e$N$h$&$JHsJ*M}E*$J2r$r@8$8$J$$$h$&(B $B$KCm0U$7$J$1$l$P$J$i$J$$(B. $B$9$J$o$A(B,

$B$H$$$&>r7o$rK~$?$9$h$&$K(B $f_{i\pm \frac{1}{2}}$ $B$r2C$($J$1$l$P$J$i(B $B$J$$(B. $B$=$3$G0J2<$N$h$&$JJd@5%U%i%C%/%9(B( corrected flux ) $f^{c}_{i\pm \frac{1}{2}}$ $B$r?7$?$KDj5A$7(B, $B$3$l$r(B(8)$B<0$N(B $f_{i\pm \frac{1}{2}}$ $B$HCV$-49$($FMQ$$$k$3$H$K$9$k(B.

$\begin{displaymath} f^{c}_{i+\frac{1}{2}} \equiv S_{i+\frac{1}{2}} \mbox{max} ... ...{1}{2}}\vert, \; S_{i+\frac{1}{2}}\Delta _{i+\frac{3}{2}})\}, \end{displaymath}$

(10')

$\begin{displaymath} \Delta _{i+\frac{1}{2}} = \rho _{i+1}^{n+1}-\rho _{i}^{n+1}, \end{displaymath}$

(11')

$\begin{displaymath} S = \left\{ \begin{array}{lcl} +1 & \mbox{if} & f_{i+\fr... ... -1 & \mbox{if} & f_{i+\frac{1}{2}} < 0 \end{array} \right. \end{displaymath}$

(12')

**$B?^(B 3:** $BJQ?t$Net al.(1973),$B?^(B6$B$r4p$K:n@.(B)
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