$B METEOR $B>e$X(B: $B<+F0I>2A(B $BLa$k(B: $B<+F0I>2A(B   $BL\

BLEU

BLEU[8]$B$O!$5!3#K]Lu$NJ,Ln$K$*$$$F!$:G$b0lHLE*$J<+F0I>2A4p=`$G$"$k!%(BBLEU$B$O!$(Bn-gram$B%^%C%AN($K4p$E$/

$${\mathrm {BLEU}} = {\mathrm {BP_{BLEU}}} * exp(\frac{1}{N} \sum^N_{n=1} \log{p_n})$$ (3.1)

$B=PNO$5$l$kCM$NNN0h$O(B0$B!A(B1$B$G$"$j!$9b$$$[$IK]LuJ8$,@52rJ8$K6a$$$3$H$r<($9!%(B(3.1)$B<0$N(BN$B$K$O!$0lHLE*$K(B$N = 4$ $B$,MQ$$$i$l$k!%(B ${\mathrm {BP_{BLEU}}}$ $B$OK]LuJ8$,@52rJ8$HHf3S$7$FC;$$>l9g$KMQ$$$k%Z%J%k%F%#78?t$G$"$k!%$3$N%Z%J%k%F%#$O!$K]LuJ8$,@52rJ8$h$j$bC;$$>l9g$KE,9gN($,9b$/$J$kLdBj$r2sHr$9$k$?$a$KMQ$$$i$l$k!%(B ${\mathrm {BP_{BLEU}}}$ $B$OK]LuJ8$NC18l?t$r(B$c$ $B!$@52rJ8$NC18l?t$r(B$r$ $B$H$7!$0J2<$N<0$G7W;;$5$l$k!%(B

$${\mathrm {BP_{BLEU}}} = \left \{ \begin{array}{l} 1 \ \ \ \ \ \ \ (c > r)\\ e^{1-\frac{r}{c}} \ \ \ (c \leq r) \end{array} \right.$$ (3.2)

$BK]LuJ8$NJ8;z?t$,@52rJ8$h$j$bD9$$>l9g$K$O!$(B ${\mathrm {BP_{BLEU}}} = 1$ $B$H$J$j!$1F6A$r5Z$\$5$J$$!%K]LuJ8$NJ8;z?t$,@52rJ8$h$j$bC;$$>l9g$K$O!$$=$NC;$5$K1~$8$F!$(B ${\mathrm {BP_{BLEU}}}$ $B$,>.$5$/$J$j!$7k2L$H$7$F(BBLEU$BCM$,>.$5$/$J$k!%$J$*!$C18l?t(B$c$ $B$H(B$r$ $B$r;;=P$9$k$H$-$NBP>]J8$O(B1$BJ8$G$O$J$$$?$a!$3FJ8$ND9$5$N<+M3EY$O;D$5$l$F$$$k!%$^$?!$(B(3.1)$B<0$N;X?t4X?t(B$p_n$ $B$O0J2<$N<0$G7W;;$5$l$k!%(B

$$p_n = \frac{\sum_{\mbox{$BA4K]LuJ8(B}} \sum_{\mbox{$B@52rJ8(B}} \mbox{$B@5(B.. ...} {\sum_{\mbox{$B%A%(%R%s%UuJ8}(B} \sum_{\mbox{$B@52rJ8(B}} \mbox{$BA4(B {\it N}-gram\mbox{$B?t(B}}}$$ (3.3)

$p_n$ $B$O@52rJ8$H0lCW$9$k(BN-gram$B?t$r%+%&%s%H$9$k$H$-!$@52rJ8$NMWAG$r=EJ#$7$F?t$($k$3$H$r2sHr$9$k$?$a$N=hM}$G$"$k!%$^$?!$@52rJ8$KBP$7$F!$K]LuJ8$NJ}$,D9$$>l9g$K$O!$(B$p_n$ $B$NCM$O>.$5$/$J$k$?$a!$(BBLEU$BCM$b>.$5$/$J$k!%(B