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发表于 2013-9-3 23:16:14
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显示全部楼层
受到mathe的启发,得到 $A_n$的特征多项式为 f(n,x) = x ChebyshevU[n,x/2-1]- Table[{n+1,Expand[x ChebyshevU[n,x/2-1]]},{n,20}]
复制代码 展开算得:- {2,-2 x+x^2}
- {3,3 x-4 x^2+x^3}
- {4,-4 x+10 x^2-6 x^3+x^4}
- {5,5 x-20 x^2+21 x^3-8 x^4+x^5}
- {6,-6 x+35 x^2-56 x^3+36 x^4-10 x^5+x^6}
- {7,7 x-56 x^2+126 x^3-120 x^4+55 x^5-12 x^6+x^7}
- {8,-8 x+84 x^2-252 x^3+330 x^4-220 x^5+78 x^6-14 x^7+x^8}
- {9,9 x-120 x^2+462 x^3-792 x^4+715 x^5-364 x^6+105 x^7-16 x^8+x^9}
- {10,-10 x+165 x^2-792 x^3+1716 x^4-2002 x^5+1365 x^6-560 x^7+136 x^8-18 x^9+x^10}
- {11,11 x-220 x^2+1287 x^3-3432 x^4+5005 x^5-4368 x^6+2380 x^7-816 x^8+171 x^9-20 x^10+x^11}
- {12,-12 x+286 x^2-2002 x^3+6435 x^4-11440 x^5+12376 x^6-8568 x^7+3876 x^8-1140 x^9+210 x^10-22 x^11+x^12}
- {13,13 x-364 x^2+3003 x^3-11440 x^4+24310 x^5-31824 x^6+27132 x^7-15504 x^8+5985 x^9-1540 x^10+253 x^11-24 x^12+x^13}
- {14,-14 x+455 x^2-4368 x^3+19448 x^4-48620 x^5+75582 x^6-77520 x^7+54264 x^8-26334 x^9+8855 x^10-2024 x^11+300 x^12-26 x^13+x^14}
- {15,15 x-560 x^2+6188 x^3-31824 x^4+92378 x^5-167960 x^6+203490 x^7-170544 x^8+100947 x^9-42504 x^10+12650 x^11-2600 x^12+351 x^13-28 x^14+x^15}
- {16,-16 x+680 x^2-8568 x^3+50388 x^4-167960 x^5+352716 x^6-497420 x^7+490314 x^8-346104 x^9+177100 x^10-65780 x^11+17550 x^12-3276 x^13+406 x^14-30 x^15+x^16}
- {17,17 x-816 x^2+11628 x^3-77520 x^4+293930 x^5-705432 x^6+1144066 x^7-1307504 x^8+1081575 x^9-657800 x^10+296010 x^11-98280 x^12+23751 x^13-4060 x^14+465 x^15-32 x^16+x^17}
- {18,-18 x+969 x^2-15504 x^3+116280 x^4-497420 x^5+1352078 x^6-2496144 x^7+3268760 x^8-3124550 x^9+2220075 x^10-1184040 x^11+475020 x^12-142506 x^13+31465 x^14-4960 x^15+528 x^16-34 x^17+x^18}
- {19,19 x-1140 x^2+20349 x^3-170544 x^4+817190 x^5-2496144 x^6+5200300 x^7-7726160 x^8+8436285 x^9-6906900 x^10+4292145 x^11-2035800 x^12+736281 x^13-201376 x^14+40920 x^15-5984 x^16+595 x^17-36 x^18+x^19}
- {20,-20 x+1330 x^2-26334 x^3+245157 x^4-1307504 x^5+4457400 x^6-10400600 x^7+17383860 x^8-21474180 x^9+20030010 x^10-14307150 x^11+7888725 x^12-3365856 x^13+1107568 x^14-278256 x^15+52360 x^16-7140 x^17+666 x^18-38 x^19+x^20}
- {21,21 x-1540 x^2+33649 x^3-346104 x^4+2042975 x^5-7726160 x^6+20058300 x^7-37442160 x^8+51895935 x^9-54627300 x^10+44352165 x^11-28048800 x^12+13884156 x^13-5379616 x^14+1623160 x^15-376992 x^16+66045 x^17-8436 x^18+741 x^19-40 x^20+x^21}
复制代码 于是最大的特征值 就是上面的方程的最大根了,算得的答案与7#完全吻合:- Table[{n+1,N[Max[x/.Solve[ ChebyshevU[n,x/2-1]==0,x,Reals]],20]},{n,50}]//Column
复制代码- {2,2.0000000000000000000}
- {3,3.0000000000000000000}
- {4,3.4142135623730950488}
- {5,3.6180339887498948482}
- {6,3.7320508075688772935}
- {7,3.8019377358048382525}
- {8,3.8477590650225735123}
- {9,3.8793852415718167681}
- {10,3.9021130325903071442}
- {11,3.9189859472289947798}
- {12,3.9318516525781365735}
- {13,3.9418836348521040543}
- {14,3.9498558243636472140}
- {15,3.9562952014676112759}
- {16,3.9615705608064608983}
- {17,3.9659461993678035566}
- {18,3.9696155060244161187}
- {19,3.9727226068054447472}
- {20,3.9753766811902754524}
- {21,3.9776616524502570901}
- {22,3.9796428837618654648}
- {23,3.9813718920726615047}
- {24,3.9828897227476208223}
- {25,3.9842294026289556621}
- {26,3.9854177481961079856}
- {27,3.9864767154838859771}
- {28,3.9874244197864851671}
- {29,3.9882759143087192179}
- {30,3.9890437907365466738}
- {31,3.9897386467837902926}
- {32,3.9903694533443937725}
- {33,3.9909438451461692095}
- {34,3.9914683525900690437}
- {35,3.9919485879904780592}
- {36,3.9923893961834910646}
- {37,3.9927949770850530033}
- {38,3.9931689860133396996}
- {39,3.9935146162684199712}
- {40,3.9938346674662559524}
- {41,3.9941316023674809243}
- {42,3.9944075943623602965}
- {43,3.9946645673271033456}
- {44,3.9949042292205070827}
- {45,3.9951281005196484952}
- {46,3.9953375383810783969}
- {47,3.9955337572463063191}
- {48,3.9957178464772070135}
- {49,3.9958907855006726840}
- {50,3.9960534568565431239}
- {51,3.9962066574740881563}
复制代码 |
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