æ¡ä»¶ä»ã確çå ´ã®ãã«ã³ãæ§ã¨ãæºãã«ã³ãé£éã¨ã
ãå®è£
ããä¸ã§ã¯ã©ãã§ããããè¨èã®å®ç¾©ã®åé¡ã®ã¨ããã«è¶³ãçªã£è¾¼ã¿ã¤ã¤ãããããªæ°ãããããã©ãCRFã«ã¤ãã¦èª¿ã¹ã¦ãããã©ãã©ãæ··ä¹±ãã¦ããã®ã§ãç¾å¨ã®ã¨ããã®ç解ãã¾ã¨ãã¦ã¿ãããã¶ããçªã£è¾¼ã¿ã©ããã¯ãã£ã±ãããã¾ãã®ã§ãçªã£è¾¼ãã§é ããã¨å¹¸ãã§ãã
ãCRFã¯å
¥åXã¨åºåYã®çµãããããä¸ãããã¨ã§ãæªç¥ã®Xã«å¯¾ãã¦ãP(Y|X)ãè¨ç®ã§ããããã«ããã¢ãã«ã§ããããã ããYã¯æ§é ãæã¤ï¼ãã®æ§é ãæã¤ã¨ããã®ãã©ãè¨ããã¨ãããããããã¦ä»èª¿ã¹ã¦ããã®ã ãããã¡ãã¯ã¨ããããæ£ä¸ãããï¼ãã®ã¨ããã
ãCRFã¯ã§ããã¨ãããã¨ããè¦å®ãããèªç¶è¨èªå¦çã§ã¯linear chain CRFã¨semi markov CRFã®2ã¤ãç¹ã«linear chain CRFããã使ããã¦ããã
ãlinear chain CRFã¯åºåYãä¸æ¬éã®æ§é ã«ãªã£ã¦ããã¨ãããç¹å¾´ã§ãããlinear chain CRFã¯ãã«ã³ãé£éã§ããã¨è¨ã£ã¦ããã®ã ãããï¼
ããã«ã³ãé£éã¯ããã«ã³ãéç¨ï¼ãã«ã³ãæ§ãæã¤ç¢ºçéç¨ï¼ã®ãã¡ãç¶æ
ãé¢æ£çãªãã®ã®ãã¨ã§ããã
ããã«ã³ãæ§ã¨ã¯ãç¾å¨ã®ç¶æ
ã決ã¾ãã°ãæªæ¥ã®ç¶æ
ã®ç¢ºçåå¸ã¯éå»ã®ç¶æ
ã«ä¾åããã«æ±ºã¾ããã¨ããæ§è³ªã§ãããCRFã«ããã¦ã¯ã®åå¸ããã®åå¸ã¨åãã«ãªããã¨è¨ããã°ããã«ã³ãæ§ãæãç«ã£ã¦ããã¨è¨ãããããã¯linear chain CRFã§ããã°æããã«æãç«ã¤ã®ã§ãlinear chain CRFã¯ãã«ã³ãé£éã§ããã¨è¨ããããªããlinear chain CRFã®å ´åã¯æéã«å¯¾ãã¦ãé¢æ£çã§ããã
ãã¯æ£è¦åé
Zãªãã§ã¯ç¢ºçã¨ãã¦ã¯æ£ãããªãã®ã§ãã®è¨ç®ããªãã ããã¾ããããªããããªæ°ãä¸ç¬ããããæ®éã«ããY_i以å¤ã®Yãç©åæ¶å»ãã¦ããã°P(Y_i|X)ã¯è¨ç®ã§ããã®ã§ãCRFã¯ãã«ã³ãé£éã§ããã¯ãã ã
ã次ã«ãsemi markov CRFã«ã¤ãã¦èãããsemi markov CRFã¯æºãã«ã³ãé£éã§ãããããªæ§é ãæã¤CRFã§ãããæºãã«ã³ãé£éã«é¢ãã¦ã¯ãã¡ããã¨ããæç§æ¸ã調ã¹ã¦ã¿ãã¨ãªããé£ãããã¦æ¯ãç«ããªãããSarawagiãã®è«æ(pdf)ã§ã¯P(Y|X)ã®ä»£ããã«P(S|X)ãæ大åããããSã¯ã»ã°ã¡ã³ãã§<éå§ä½ç½®, çµäºä½ç½®, ã©ãã«>ã®3ã¤çµã§æ§æãããããã¨ããsemi markov CRFã®å®ç¾©ãããªããæºãã«ã³ãé£éèªä½ã®å®ç¾©ã¯æ¸ãã¦ãªãã
ãwikipediaã®準マルコフ過程ã®ãã¼ã¸ãè¦ãã¨ããã«ããã¨ãæºãã«ã³ãéç¨ã§ã¯ãç¶æ
ã«å¯¾ãã¦æ»çæéãèãããã¤ã¾ããããç¶æ
ã«ä¸å®æéçã¾ã£ãã¾ã¾ããããã¨ããã¢ãã«ã§ãããæºãã«ã³ãéç¨ã§ã¯ã
- ç¶æ ãã¸ã£ã³ããã確çéç¨ã¯ãã«ã³ãé£é
- æ»çæéããµã³ããªã³ã°ããåå¸ã¯ãªãã§ããã
ãã¨ããæ¡ä»¶ãã¤ããï¼2ã¤ç®ã¯æ¡ä»¶ã¨ã¯è¨ããªããâ¦ãï¼ãã®1ã¤ç®ã®ãã«ã³ãé£éã¨2ã¤ç®ã®æ»çæéã決å®ãã確çåå¸ã®2ã¤ãåããã¦æºãã«ã³ãéç¨ã¨ããã
ããã®wikipediaã®å®ç¾©ã¨ãSarawagiãã®å®ç¾©ã«ã¯ãç§ã®ç®ããã¯é£ãéã£ã¦ããããã«ã¯è¦ããªãã®ã§ã以ä¸ã¯ãã®å®ç¾©ãæ¡ç¨ãã¦è©±ãããããã
ãsemi markov CRFã§ã¯ãç¶æ
ãã¸ã£ã³ããã確çéç¨ã¯ãã«ã³ãé£éã§ããã¨è¨ããã®ã ãããï¼linear chain CRFã®å ´åã¨åãããç©åæ¶å»ãã¦ããã°ãã«ã³ãæ§ãè¨ãã¦ããã«ã³ãé£éã§ãããã¨è¨ããã¨æãã®ã ãããªãã ãèªä¿¡ãæã¦ãªããããããã«ã³ãé£éã§ããã¨è¨ãã¦ãã¾ãã¨ãã©ãã«ãã¤ã¢ã¹ã®è©±çã«ãªãããã¾ããªãæ°ãããããããã¯ãªã¢ã«ãªãã°ãCRFãç解ã§ããã¨è¨ã£ã¦ããããããªæ°ããããã ãã©â¦ã
ã追è¨ï¼@nokunoãããã CRFみたいな識別モデルもマルコフ連鎖って呼ぶんでしたっけ? マルコフ連鎖は生成モデルの印象が… ã¨ããæè¦ãããã ãã¾ãããHMMã¨MEMMã¨CRFã®ã°ã©ãã£ã«ã«ã¢ãã«ã並ã¹ã¦çºãã¦ããã¨ãæ£ç´ã©ãã©ãã¨ããããããªããªã£ã¦ããã®ã§ãããå®ç¾©ãè¦ãéãã§ã¯ãã«ã³ãé£éã¯ç¶æ
空éãé¢æ£çãªãã«ã³ãéç¨ã§ãããã¨ããäºããæ¸ãã¦ãªãã®ã§ããã«ã³ãæ§ãæºãã確çéç¨ã§ããã°ãªãã§ããã«ã³ãé£éã£ã¦å¼ã¹ãããããªããã¨æãã¾ãããã ãCRFã確çéç¨ã«ãªã£ã¦ããã®ãã©ããã¯ãç§ã«ã¨ã£ã¦ã¯èªæã§ãªãã®ã§ãããã辺ã¯èããå¿
è¦ãããã¾ããã