Re: [理工] [線代] 100台大
※ 引述《a942195 (roseeeee)》之銘言:
: Pn = [ 1/2 1/3 … 1/n+1]
: [ 1/3 1/4 … 1/n+2]
: [ . . . ]
: [ . . . ]
: [1/n+1 1/n+2 .. 1/2n ] then det(Pn+1)/det(Pn) =?
---
我做一次 n=4 的 case
剩下可以類推:
│ 1/2 1/3 1/4 1/5 │
│P_4│ = │ 1/3 1/4 1/5 1/6 │
│ 1/4 1/5 1/6 1/7 │
│ 1/5 1/6 1/7 1/8 │
│ 3/(2*5) 3/(3*6) 3/(4*7) 3/(5*8) │
= │ 2/(3*5) 2/(4*6) 2/(5*7) 2/(6*8) │
│ 1/(4*5) 1/(5*6) 1/(6*7) 1/(7*8) │
│ 1/5 1/6 1/7 1/8 │
3!4! │ 1/2 1/3 1/4 1/5 │
= ── * │ 1/3 1/4 1/5 1/6 │
8! │ 1/4 1/5 1/6 1/7 │
│ 1 1 1 1 │
3!4! │ 3/(2*5) 2/(3*5) 1/(4*5) 1/5 │
= ── * │ 3/(3*6) 2/(4*6) 1/(5*6) 1/6 │
8! │ 3/(4*7) 2/(5*7) 1/(6*7) 1/7 │
│ 0 0 0 1 │
3!4! 3!4! │ 1/2 1/3 1/4 1 │
= ── *── │ 1/3 1/4 1/5 1 │
8! 7! │ 1/4 1/5 1/6 1 │
│ 0 0 0 1 │
(3!4!)^2
= ──── │P_3│
7!8!
Note: │P_(n+1)│ [n!(n+1)!]^2
───── = ───────
│P_n│ (2n+1)!(2n+2)!
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