D??[D?f(t)]?
1?????0?t???t??1D?f(?)d? (3.1.1)
??t1???D?t??Df(?)d?????0???1????其中利用定理3.1.1和分部积分法,可将式(3.1.1)中? ?内的积分计算如下:
1????1????1????1?1????1??0?t????0?t????0?t???ttt?D?f(?)d??(k??)Dk?Df(?)???d???DkdD?(k???1)f(?)kD?Df?0??t1??k??t??1?j?(k??)?t???Df(?)d?????????k?1?0????2?j?j?1k?j?(k??)ktD??jf?0???1?j1??k?(k??)?f(?)d???t?t???D?0????k?1?j?1????2?j??D????k?1???jDf?0???1?j?(k??)?f(t)??D???????2?j?tj?1kkD??jf?0???1?j ?Df(t)??????2?j?tj?1?1(3.1.2)
,k在t?0端点处都是有界
由于D?f?t?是可积的,D??jf?t?对任意的j?1,2,的,从而上式中各项都是存在的。将(3.1.2)计算的结果代入(3.1.1)可得
??jk?Df?0???1?j?????1D[Df(t)]?D?Df(t)??t????2?j??j?1?? ??jkDf?0???j?f(t)??t?k?1???k?.j?1????1?j?(3)根据Riemann-Liouville分数阶导数的定义,我们有
dnD[?f(x)??g(x)]?ndx???x1n???1??x???f(?)??g(?)d????????0?n????????xdn1n???1??nx??f(?)d???dx??n????0xdn1n???1+?nx??g(?)d???dt??n????0
??D?f(x)??D?g(x)
3.1.2 若?????,且满足0???1,cosx和sinx可表示为
??xkxk cosx??ak,sinx??bkk!k!k???k???其中:a2k?1?0,a2k?b2k?1?(?1)k,b2k?0(k?),则
D?sinx?sin(x???2),D?cosx?cos(x???2).[6]
3.1.3 设???,且满足0???1,如果f(x)?C1(),则有
(1)D?[f(?x)]???D?f(u)|u??x;(2)D??f(x)??D1??f(x)dx;(3)D??[f(?x)]?1
??D??f(u)|u??x.证明:
(1)D?[f(?x)]?u??s1d?(1??)dx?x0f(?s)ds?(x?s)
???1d?xf(u)??du?(1??)dx?0(?x?u)??x??df(u)??du?(1??)d(?x)?0(?x?u)????D?f(u)|u??x特别地,有D?e?x???e?x。
(2)D?[f(x)]?(D?1??f(x))?,于是,D?1??f(x)??D?f(x)dx,故而,
D??f(x)??D1??f(x)dx;
(3)D??[f(?x)]??D1??[f(?x)]dx????D1??f(u)|u??x?
1???D?f(u)du?1??If(u)|u??x.?
3.1.4 设???,且满足0???1,则有
(1)D?sin?x???sin(?x?(2)D??sin?x??证明:
?2??);D?cos?x???cos(?x??);21??11???)?C;D??cos?x???sin(?x??)?C.2?21??cos(?x?(1) 由3.1.2和3.1.3易得结论。
(2)D??sinx??D1??sinxdx??sin(x?1??1???)dx??cos(x??)?C2211??D??sin?x??D1??sin?xdx???cos(?x??)?C?21??1????1??Dcosx??Dcosxdx??cos(x??)dx?sin(x??)?C 2211??D??cos?x??D1??cos?xdx??sin(?x??)?C?23.2分数阶导数在其他定义下运算法则的探讨
根据上一小节Riemann-Liouville定义下的定理3.1.1,我们思考其在Grünwald-Letnikov、Caputo、Weyl定义下是否仍然成立呢?初步研究表明,定理3.1.1在其他定义下是不成立的,而下面的运算法则又是基于此定理证明而来,所以我们得出了其他三种分数阶导数定义下并不满足这些运算法则。具体的证明方法此文还并未给出,需要日后再做进一步的努力。
4 分数阶导数和积分的基本性质
4.1 Riemann-Liouville分数阶导数定义下分数阶微积分的性质
性质4.1.1 如果R????0,则有
??
??Da??t?a???1?x???????????1?x?a???????????????1?x?a??????? R????0, (4.1.1)
4.1.2) R????0, (
?Da??t?a???1?x???特别地,取??1,且R????0,则表明一个常数的Riemann-Liouville分数阶导数通常不等于0,
x?a??? ?Da?1??x????1?????,0?R????1 . (4.1.3)
?,如果分数阶导数?DmDa?y??x?和
性质4.1.2 令R(?)?0,m?且D?ddx?D??ma?y??x?存在,那么有
???m ?DmDa(4.1.4) ?y??x???Da?y??x?
?1???m,(n,?m性质4.1.3 令??0且??0满足n?1???n,m)且,
????n,并且令f?L1?a,b?,fm???ACm??a,b??.那么我们有下面的指数规律:
?x?a????????jfx?Dfx?Dfa? ?Da?Da ????????a????a???1?j??? (4.1.5)??j?1m?j??
4.2 分数阶导数 、积分的奇偶性及周期性
定理4.2.1 设???,且满足0???1,如果f(x)?C1()是奇函数(或偶函数),
那么D?f(x),D??f(x)不再具有奇偶性。

