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发表于 2018-3-29 07:13
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本帖最后由 elim 于 2018-3-30 07:19 编辑
我要回答第二楼的问题:为什么 na(n) 似乎总是小于 2? 2 是不是 na(n) 的上界?
其实 11 楼已经否定了这些基于小 n 的计算,下面是更精细的分析结果:
下面是一些计算验证:
- Reading GPRC: gprc.txt ...Done.
- GP/PARI CALCULATOR Version 2.9.3 (released)
- i686 running mingw (ix86/GMP-6.0.0 kernel) 32-bit version
- compiled: Jul 4 2017, gcc version 4.9.1 (GCC)
- threading engine: single
- (readline v6.2 enabled, extended help enabled)
- Copyright (C) 2000-2017 The PARI Group
- PARI/GP is free software, covered by the GNU General Public License, and comes
- WITHOUT ANY WARRANTY WHATSOEVER.
- Type ? for help, \q to quit.
- Type ?15 for how to get moral (and possibly technical) support.
- parisize = 4000000, primelimit = 500000
- (15:56) gp > \p 72
- realprecision = 77 significant digits (72 digits displayed)
- (15:56) gp > \\ Set up 72+ precision positions
- (15:56) gp > \\ Define a(n) as recursion result:
- (15:56) gp > a(n)=my(v=0.5);for(k=1,n,v=log(1.+v));return(v);
- (15:57) gp > \\ Define na(n):
- (15:57) gp > na(n) = n*a(n)
- %2 = (n)->n*a(n)
- (15:57) gp > m = 8888888
- %3 = 8888888
- (15:57) gp > aaa = a(m)
- %4 = 2.25000044216132665030532250842813971976969537059565617775003653663212045 E-7
- (15:59) gp > \\ Init c
- (15:59) gp > c = ((2./3)*log(m)-m*(m*aaa-2.))/4
- %5 = 2.23775823755171563893482900512968124519988881536917722052013201695027518
- (15:59) gp > \\ Set some constants by c
- (16:27) gp > cc()=c1=-4*c;c2=2.;c3=(c1-2.)/3;c4=((12.+72*c)*c+1.)/9;c5=-5./3;c6=4*(15*c+2)/9;c7=-((300+1800*c)*c+29)/270;
- (16:06) gp > \\ Define asymtotic nb(n) for na(n):
- (16:27) gp > nb(n)=my(q=log(n)/3./n);return(2.+(c1+(c4+c7/n)/n/n)/n+q*(2.+(c3+c6/n)/n/n+(c2+c5/n)*q/n));
- (16:08) gp > \\ Define asymtotic b(n) of a(n):
- (16:09) gp > b(n)=nb(n)/n
- %8 = (n)->nb(n)/n
- (16:09) gp > cc()
- %9 = -35.9775516473352732305837941091705122983421448034777965638690077960996251
- (16:09) gp > \\ Refine c:
- (16:10) gp > rc()=c=(c-m^2*(b(m)-aaa)/((48*c+4-8*log(m))/3./m-4.+(20*log(m)-12>
- (16:12) gp > ref()=my(v=c);for(k=1,7,v=rc());return(v)
- %11 = ()->my(v=c);for(k=1,7,v=rc());return(v)
- (16:13) gp > ref()
- %12 = 2.23775823755197059127070078839538197874637052643388424195634588475419378
- (16:13) gp > ref()
- %13 = 2.23775823755197059127070078839538197874637052643388424195634644606476959
- (16:13) gp > b(m)
- %14 = 2.25000044216132665030532250842813971976969537059565617775003653663212045 E-7
- (16:13) gp > aaa
- %15 = 2.25000044216132665030532250842813971976969537059565617775003653663212045 E-7
- (16:13) gp > na(677760)
- %16 = 1.99999999999918546366306865085828226409641238635664971790415445534421476
- (16:14) gp > na(677761)
- %17 = 2.00000000000063675950453735968329108478827481760924704645452559292323738
- (16:14) gp > nb(677760)
- %18 = 1.99999999999911164393231235515404685157428912958719201482877867167049023
- (16:14) gp > nb(677761)
- %19 = 2.00000000000056294095274137028255081535172203855123432637250222648870740
- (16:15) gp > m = 1842344
- %20 = 1842344
- (16:21) gp > aaa = a(m)
- %21 = 1.08557379178794303415323838093593433837841534725660910882529881216105801
- E-6
- (16:22) gp > ref()
- %22 = 2.23775825092018944161885973473185509866717805839259579758945362416830970
- (16:22) gp > b(m)
- %23 = 1.08557379178794303415323838093593433837841534725660910882529891215708435 E-6
- (16:23) gp > aaa
- %24 = 1.08557379178794303415323838093593433837841534725660910882529881216105801 E-6
- (16:23) gp > ref()
- %25 = 2.23775825092018944161885973473185509866717805839259579767430603764714274
- (16:23) gp > b(m)
- %26 = 1.08557379178794303415323838093593433837841534725660910882529881216105801 E-6
- (16:23) gp > aaa
- %27 = 1.08557379178794303415323838093593433837841534725660910882529881216105801 E-6
- (16:24) gp > na(677760)
- %30 = 1.99999999999918546366306865085828226409641238635664971790415445534421476
- (16:24) gp > nb(677760)
- %31 = 1.99999999999903274745656801272354020886384772584741900083190384555939479
- (16:24) gp > nb(1842343)
- %32 = 2.00000036185776612120698279212895889695791338052604291704079874145024171
- (16:25) gp > nb(1842344)
- %33 = 2.00000036185776612131401381168703301270544324452613025198963631479205226
- (16:25) gp > nb(1842345)
- %34 = 2.00000036185776612131443511055947138143016491731739291448548380991427976
- (16:25) gp > nb(1842346)
- %35 = 2.00000036185776612120824697807754681786496038421933904449877689257619287
- (16:25) gp > na(1842344)
- %36 = 2.00000036185776612131401381168703301270544324452613025198963631479205226
- (16:26) gp > na(1842345)
- %37 = 2.00000036185776612133221538678489460866457882999723176943891566123318151
- (16:26) gp > na(1842346)
- %38 = 2.00000036185776612124380751120749492406307983911995621444886516181213986
- (16:27) gp >
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