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¡ï Сľ³æ: ½ð±Ò+0.5, ¸ø¸öºì°ü£¬Ð»Ð»»ØÌû
Äã˵µÄÒâ˼ÆäʵÓеãÏñuniform convergence, Ò²¾ÍÊÇÖ¸Ïȹ̶¨partial sumµÄÏîÊýN, È»ºóÈ¥checkÿһµãÊÇ·ñ¶¼"ÊÕÁ²"(Àëf(x)º¯ÊýÖµºÜ½ü). µ«ÊÂʵÉÏDirichlet¶¨Àí˵µÄ²»ÊÇuniform convergence, ¶øÊÇPOINTWISEÊÕÁ². POINTWISEÊÕÁ²Ö¸µÄÊÇÎÒÿ´Î¶¼¹Ì¶¨Ò»µã¿´, ÈçÁ¬Ðøµãx_0, ÄÇôS(x_0)À뺯Êýf(x_0)¶à½üÄØ? ÕâÒª¿´N¶à´ó, Èç¹ûÕâµãµÄÖµS(x_0)Àëf(x_0)ºÜÔ¶, ÎÒ¾ÍÔö´óN. Dirichlet¶¨Àí˵ÎÒ×ÜÄÜÕÒµ½Ò»¸ö×ã¹»´óµÄNʹµÃS(x_0)Àëf(x_0)×ã¹»½ü. ËùÒÔÕâ¸öNÊǺÍx_0ÓйصÄ.
ÀýÈçÄã˵µÄstep function, ÔÚx=1´¦, ¿ÉÄÜN=100¾ÍÓÐS(1)ºÍf(1)×㹻СÁË; µ«ÊÇÔÚx=0.01, Õâ¸öN¿ÉÄÜÒª10000; ¶øÔÚx=0.0001, Õâ¸öN¿ÉÄܾÍÒª¸ü´ó. ÎÞÂÛÄ㿼ÂǵÄxÓжàô½Ó½ü0, ÒòΪËüÊÇÁ¬Ðøµã, ×ÜÄÜÕÒµ½Ò»¸öN(ºÜ´óºÜ´óºÜ´ó, ÒÀÀµÓÚxµÄÑ¡Ôñ), ʹµÃS(x)Àëf(x)×ã¹»½ü.
×¢Òâ, ÕâÀïÎÒÃÇÊÇÖ»¿´Ò»¸öµã, ¶øÑ¡ÔñʹµÃÔÚÕâ¸öµãÏÂpartial sum"ÄÜ¿¿½ü"fº¯ÊýÖµµÄN, ÆäËüµãÔÚÕâ¸öNÏ¿¿²»¿¿½üfÎÒÃDz»¹Ü. Èç¹ûÎÒÃÇÐèÒª¹Û²ìÆäËüµã, ÄÇô¾ÍÒªÖØÐÂΪËù¹Û²ìµÄµãÑ¡Ôñ×ã¹»´óµÄN. ÕâÊÇPOINTWISEÊÕÁ²µÄ"¾«Ëè".
ÏÖÔÚ»ØÀ´¿´¿´overshootÔÚÄÄÀï. ÉÏÃæµÄÀý×Ó, ÔÚx=1´¦, overshoot¿ÉÄÜÔÚ0.01¸½½ü(¼ÙÉèµÄ); ¶øÔÚx=0.01, ÔÚ¸Õ²Å˵ÁËN=100ʱovershoot¸ÕºÃÔÚÕâÀï, ÄÇÏÖÔÚÎÒÃǸÃÔõô°ì? Ñ¡ÔñN=10000, ´ËʱovershootÏò×óÒƶ¯ÁË(¿ÉÄÜÒƶ¯µ½ÁË0.0001¸½½ü), ʹµÃÔÚx=0.01´¦ÄÜÊÕÁ²ÁË... ÒòΪÕâ¸öovershootµÄÒƶ¯, ËùÒÔÎÞÂÛÎÒÃÇ¿¼ÂÇÄĸöÁ¬Ðøµã(Õâ¸öÁ¬ÐøµãÈçºÎ½Ó½üx=0), ÎÒÃǶ¼ÄÜ°ÑovershootÔÙÏòԵ㴦Òƶ¯(ÕâÊÇÒòΪʵÊýÊÇdenseµÄ, Ò»¸ö´óÓÚ0µÄÊý, ËüµÄ×ó±ß×ÜÊÇ»¹ÓдóÓÚ0µÄÊý, ËùÒÔovershoot»¹ÄÜÍù×óÒÆ).
BTW, ÎÒÒ²²»ÊÇÊýѧ³öÉíµÄ...
Remark: ÎÒ¿´ÁËÄã·¢µÄÌû×Ó, ÄãËƺõ¶ÔÊÕÁ²Õâ¸ö¸ÅÄî²»ÊǺÜÇå³þ. Äã¿ÉÒÔÏȸ´Ï°Ò»Ï¼«ÏÞµÄ(¦Å, ¦Ä)-definition. |
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