北大数学物理方法(B)教案09二阶线性常微分方程的幂级数解法2

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WuChong-shi()1!#$%()§9.1&’()*+,-./01234567859:;785=?@AB7859CD=AB745EF685GH=AB7I59JKL:;MN85OPQRB7STGUVCWXYZ[\]^_‘abcd9.1efz0A:;d2wdz2+p(z)dwdz+q(z)w=0785GNLp(z)gq(z)hBi7jklP0|z−z0|RQG:;7m_n6opBAw1(z)=(z−z0)ρ1∞Xk=−∞ck(z−z0)k,w2(z)=gw1(z)ln(z−z0)+(z−z0)ρ2∞Xk=−∞dk(z−z0)k,qrρ1,ρ2gghAst9Fefρ1Eρ2AutGvg=0GNz05K:;7B745EF6859Fefρ1Eρ2CAutGEg6=0GN:;7BKwxytGz05KqI59z{|}~GG¡9¢£⁄¥ƒ§G¤'“«G‹›fifl–†‡·†‡G¶•‚„”»…‰9ef¿tBr1`_´ˆ˜G¯?˘˙¨u˚7ρxG¸¿tBr˝´ˆ˜Gw1(z)=(z−z0)ρ1∞Xk=0ck(z−z0)k,w2(z)=gw1(z)ln(z−z0)+(z−z0)ρ2∞Xk=0dk(z−z0)k.˛AGˇ—p˙Rt79GH‘Æρx9⁄ª£()09g6=0¥Gw2(z)ª·w1(z)(Ł›Ø‡)G¢Œº9g=0¥Gw2(z)¡§ŁØ‡Gª9:;85OPQm_n6opBhAMNB7æGı7‘a(CX)bWuChong-shi§9.1łøœß2cd9.2:;d2wdz2+p(z)dwdz+q(z)w=0,L785z07OP0|z−z0|Rm_MNBw1(z)=(z−z0)ρ1∞Xk=0ck(z−z0)k,c06=0,(9.1)w2(z)=gw1(z)ln(z−z0)+(z−z0)ρ2∞Xk=0dk(z−z0)k,gEd06=0(9.2)7Az05Ap(z)7C^745G(z−z0)p(z)Lz05Biq(z)7C745G(z−z0)2q(z)Lz05Bi9z0K:;7MN859ρ1gρ2KMNB799.1Gz=0gz=1hA:;z(1−z)d2wdz2+[γ−(1+α+β)z]dwdz−αβw=07MN85x=±1@hALegendre:;1−x2d2ydx2−2xdydx+l(l+1)y=07MN859Ko5AKMN85GJz=1/tGeft=0A7:;7MN85Gt=05A7:;785Gvt2t−1t2p1t=2−1tp1tgt2·1t4q1t=1t2q1tLt=05BiGz=∞5A:;785Gvzp(z)gz2q(z)Lz=∞5BiGNz=∞5A7:;7MN859˙Go5z=∞@hA:;gLegendre:;7MN859WuChong-shi()3&’()*+,-.0b•MNBw1(z)Ew2(z):;•!tGRÆ#$gp•%&RÆt7’(7RB;G˘A)w1(z)k7B:;GFef=*?Rm_n6opBG+,-./0G˝Uw2(z)k7B:;9Fef¯?1=R^_B(1eρ1=ρ2?)G23GHUw2(z)k7B(¯?7g^‘CK0):;RB94Ts5æ:;7a3G6˛^_n6s5æ:;d2wdz2+p(z)dwdz+q(z)w=0,ef78RÆ^_Bw1(z)G23G˘˙9æw2(z)=Aw1(z)Zz1[w1(z)]2exp−Zzp(ζ)dζdz:RÆ;B9¯AK¯m_Bh=:;d2w1dz2+p(z)dw1dz+q(z)w1=0,d2w2dz2+p(z)dw2dz+q(z)w2=0.w2(z)gw1(z)æ?@¯m_:;GUAG-Bw1d2w2dz2−w2d2w1dz2+p(z)w1dw2dz−w2dw1dz=0,ddzw1dw2dz−w2dw1dz+p(z)w1dw2dz−w2dw1dz=0.9æGw1dw2dz−w2dw1dz=Aexp−Zzp(ζ)dζ.mCD˙w21GE˙Bddzw2w1=Aw21exp−Zzp(ζ)dζ.(9.3)U9æ^VGBF7Gf9WuChong-shi§9.1łøœß49.2RLegendre:;1−x2d2ydx2−2xdydx+l(l+1)y=0Lx=1OPQ7HB90x=1ALegendre:;7MN85GI˚Jy(x)=(x−1)ρ∞Xn=0cn(x−1)n.:;G∞Xn=0cn(n+ρ)(n+ρ+1)−l(l+1)(x−1)n+1+2∞Xn=0cn(n+ρ)2(x−1)n=0.KL˙B#$:;ρ(ρ−1)+ρ=0gpcn=−n(n−1)−l(l+1)2n2cn−1.#$:;7BAρ1=ρ2=0.⁄“MLegendre{x=1NOPQR¤STU{VP|x−1|2QWG{x=1N›XŒRYZ¤[Ł›Ø‡G\x=1(·x=−1)£]NG¢Œ{x=1(·x=−1)N^_9‘aºR¤9KpG˙RÆLegendre:;Lx=15OPQ;^B7t7˜bcn=(l+n)(l+1−n)2n2cn−1=(l+n)(l+1−n)2n2(l+n−1)(l+2−n)2(n−1)2cn−2=······=(l+n)(l+1−n)2n2(l+n−1)(l+2−n)2(n−1)2···(l+1)l2·12c0=1(n!)2Γ(l+n+1)Γ(l−n+1)12nc0.cc0=1GRÆLegendre:;7;^BPl(x)=∞Xn=01(n!)2Γ(l+n+1)Γ(l−n+1)x−12n,KlV;^dLegendreyt9efefR;BGN˚Jy2(x)=gPl(x)ln(x−1)+∞Xn=0dn(x−1)nWuChong-shi()5=g∞Xn=01(n!)2Γ(l+n+1)Γ(l−n+1)x−12nln(x−1)+∞Xn=0dn(x−1)n.ghs5æ:;¿tBi7$jklG‘Ætg(^‘CK0)gdn9m’7niA4T;Bo;^Bpq7pGrÆy2(x)=gPl(x)Zx(1[Pl(ξ)]2expZξ2ζ1−ζ2dζ#)dξ=gPl(x)Zx1[Pl(ξ)]2dξ1−ξ2=gPl(x)Zxdξ1−ξ2+gPl(x)Zx1[Pl(ξ)]2−1dξ1−ξ2,stuC;˜L|x−1|2QBiGL˙;BJKy2(x)=g2Pl(x)lnx+1x−1+∞Xn=0dn(x−1)n.cg=1Gv‘ÆdnGw˙RÆLegendre:;7;BQl(x)=12Pl(x)lnx+1x−1−2γ−2ψ(l+1)+∞Xn=01(n!)2Γ(l+n+1)Γ(l−n+1)1+12+···+1nx−12n,KlV;dLegendreytGqrγAEulertGψ(z)AΓyt76t5x9K˛ytPl(x)(yzB{|GA˙x=−1gx=∞KI57wxyt)gQl(x)7wx67}‘67~‘G¸??9WuChong-shi§9.1łøœß6ı˘G^ıRs5æ:;d2wdz2+p(z)dwdz+q(z)w=0LMN85OPQ7B7^klG?bL3ıG:;7;BC6t˜L3ıG:;7;B=6t˜L3ıG:;7;B^‘6t˜9~‘:;LMN857m_#$Reρ1≥Reρ2GNρ1−ρ26=ut?G;B^‘C6t˜ρ1=ρ2?G;B^‘6t˜ρ1−ρ2=Mut?G;B=6t˜9KGCJz=05A7MN859˛AGLz=057OPQG:;7tJLaurentp(z)=∞Xl=0alzl−1,q(z)=∞Xl=0blzl−2.JBKw(z)=zρ∞Xk=0ckzk.:;G∞Xk=0ck(k+ρ)(k+ρ−1)zk+ρ−2+∞Xl=0alzl−1∞Xk=0ck(k+ρ)zk+ρ−1+∞Xl=0blzl−2∞Xk=0ckzk+ρ=0,∞Xk=0ck(k+ρ)(k+ρ−1)zk+ρ−2+∞Xk=0kXl=0al(k+ρ−l)+blck−lzk=0.!mCwVˆGz07tGc0[ρ(ρ−1)+a0ρ+b0]=0.K˛c06=0G˙ρ(ρ−1)+a0ρ+b0=0.¯A#$:;Gqr7a0gb0Ka0=limz→0zp(z),b0=limz→0z2q(z).4T#$:;˙RÆm_#$Gρ1gρ29[Reρ1≥Reρ29WuChong-shi()7U!zn7tG(n+ρ)(n+ρ−1)cn+nXl=0al(n+ρ−l)+blcn−l=0,(n+ρ)(n+ρ−1)+a0(n+ρ)+b0cn+nXl=1al(n+ρ−l)+blcn−l=0.¯-Ætpq7p9¶•‚„G\cn¡9G{cn¡§¤[Ł›ρ9„ρ=ρ1Gw1(z)9„ρ=ρ2Gw2(z)9ρ1−ρ26=¥G()¡9ρ1=ρ2?G¯1=B^_B9˙G¯?;B^‘6t˜9ρ1−ρ2=Mutm?G6˛;B7tc(2)mG(m+ρ2)(m+ρ2−1)+a0(m+ρ2)+b0c(2)m+mXl=1al(m+ρ2−l)+blc(2)m−l=0.m+ρ2=ρ1G˙0·c(2)m+mXl=1hal(ρ1−l)+blic(2)m−l=0.LmXl=1hal(ρ1−l)+blic(2)m−l6=0?Gc(2)moBmXl=1hal(ρ1−l)+blic(2)m−l=0?Gc(2)m+9F6˛;^¢kG:;7;B@^‘6t˜9F6˛;¢kG:;7;B^‘C6t˜GH=efRB91A¯?˙7£˜tc(2)n(nm)⁄?S¥˛c0(2)gc(2)m9;Bw2(z)-m˜G^˜M!˛c(2)0G^˜M!˛c(2)m9Uƒ§æi^ıG⁄¤'Gc(2)m+ngc(2)mpq7poc(1)ngc(1)0pq7p/{^GLGoc(2)m0M!7˜M“A;^B(ww=«^_st‹t)G&Ccc(2)m=09WuChong-shi§9.2Bessel8§9.2Bessel›fiflBessel:;d2wdz2+1zdwdz+1−ν2z2w=0As7s5æ:;p^GqrνAstGReν≥09stGz=0A:;7MN85Gz=∞A:;7–MN859F†23Bessel:;Lz=057OP|z|0Q7B9Jw(z)=zρ∞Xk=0ckzk,c06=0,Bessel:;G∞Xk=0ck(k+ρ)(k+ρ−1)zk+ρ−2+∞Xk=0ck(k+ρ)zk+ρ−2+∞Xk=0ckzk+ρ−ν2∞Xk=0ckzk+ρ−2=0,}‡zρ−2G∞Xk=0ck(k+ρ)2−ν2zk+∞Xk=0ckzk+2=0.4T¿t7·^6G!t9KwVˆz0˜7tGvKc06=0GB&’Gρ

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