[x 1 0 0 0] [x 1 0 0 0]
[1 2x 1 0 ] [1/2 x 1/2 0 ]
[0 1 2x 1 ]=2^n-1[0 1/2 x 1/2 ]
[0 0 1 2x ] [0 0 1/2 x ]
[ 2x 1] [ 1/2 x 1/2]
[0 1 2x] [0 1/2 x ]
=cosnθ=Tn(x)
は第1種チェビシェフ多項式の行列式表示となる.
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第1行目が[x 1/√2 0 0 0]にならないことが気になるが,(その472)と同様に計算すると
x[x 1 0 0 0 ]-√cw [x 1 0 0 0 ]
[1/2 x 1/2 0 ] [1/2 x 1/2 0 ]
[0 1/2 x 1/2 ] [0 1/2 x 1/2 ]
[0 0 1/2 x ] [0 0 1/2 x ]
[ x 1/2 ] [ x 0 ]
[0 1/2 x ] [0 1/2 √cw]
(n-1行) (n-1行)
x[x 1 0 0 0 ]-cw [x 1 0 0 ]
[1/2 x 1/2 0 ] [1/2 x 1/2 0 ]
[0 1/2 x 1/2 ] [0 1/2 x 1/2 ]
[0 0 1/2 x ] [0 0 1/2 x 1/2]
[ x 1/2 ] [0 1/2 x ]
[0 1/2 x ]
(n-1行) (n-2行)
2^n-1をかけると
x2^n-1[x 1 0 0 0 ]-2cw2^n-2[x 1 0 0 ]
[1/2 x 1/2 0 ] [1/2 x 1/2 0 ]
[0 1/2 x 1/2 ] [0 1/2 x 1/2 ]
[0 0 1/2 x ] [0 0 1/2 x 1/2]
[ x 1/2 ] [0 1/2 x ]
[0 1/2 x ]
=xcos(n-1)θ-2cwcos(n-2)θ
=cosθcos(n-1)θ-2cwcos(n-2)θ
=cosθcos(n-1)θ-2cw{cos(n-1)θcosθ+sin(n-1)θsinθ}
=cosθcos(n-1)θ-2cos^2π/w{cos(n-1)θcosθ+sin(n-1)θsinθ}
=(1-2cos^2π/w)cosθcos(n-1)θ-2cos^2π/w・sin(n-1)θsinθ
=(1-2cos^2π/w)cosθcos(n-1)θ-2cos^2π/w・sin(n-1)θsinθ+sin(n-1)θsinθ-sin(n-1)θsinθ
=-cos2π/w・cosθcos(n-1)θ-(1+cos2π/w)・sin(n-1)θsinθ}
=-cosθcos(n-1)θ{cos2π/w+(1+cos2π/w)・tan(n-1)θtanθ}=0
-1=(1+sec2π/w)tan(n-1)θtanθ
ここに誤りがあっった.
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