Student Seminar: Classical and Quantum Integrable Systems
Student Seminar: Classical and Quantum Integrable Systems
Student Seminar: Classical and Quantum Integrable Systems
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<strong>and</strong> if k < j the contribution will be<br />
Thus, adding up we obtain<br />
O j =<br />
−<br />
=<br />
−<br />
k j +1<br />
W A j (λ k , {λ} M k+1) + W D j (λ k , {λ} M k+1) .<br />
M∏ λ j − λ k − i<br />
(λ j + i ) j−1 L ∑<br />
+ Wj A (λ k , {λ} M<br />
λ j − λ k 2<br />
k+1)<br />
k j +1<br />
k=j+1<br />
k=1<br />
M∏ λ j − λ k + i<br />
(λ j − i ) j−1 L ∑<br />
+ Wj D (λ k , {λ} M<br />
λ j − λ k 2<br />
k+1) =<br />
k=1<br />
(<br />
M∏ λ j − λ k − i<br />
(λ j + i ) j−1<br />
j−1<br />
L ∑ i ∏<br />
1 +<br />
λ j − λ k 2<br />
λ k − λ j<br />
k=1<br />
p=k+1<br />
(<br />
M∏ λ j − λ k + i<br />
(λ j − i ) j−1<br />
j−1<br />
L ∑ i ∏<br />
1 −<br />
λ j − λ k 2<br />
λ k − λ j<br />
k=1<br />
k=j+1<br />
Let us now note the useful identity<br />
p=k+1<br />
)<br />
λ j − λ p − i<br />
λ j − λ p<br />
)<br />
λ j − λ p + i<br />
.<br />
λ j − λ p<br />
t n ≡ 1 +<br />
j−1<br />
∑<br />
k=n<br />
i<br />
λ k − λ j<br />
j−1<br />
∏<br />
p=k+1<br />
j−1<br />
λ j − λ p − i ∏ λ j − λ k − i<br />
=<br />
.<br />
λ j − λ p λ j − λ k<br />
k=n<br />
We will prove this by induction over n. For n = j − 1 <strong>and</strong> n = j − 2 we have<br />
i<br />
t j−1 = 1 + = λ j − λ j−1 − i<br />
,<br />
λ j−1 − λ j λ j − λ j−1<br />
i<br />
i λ j − λ j−1 − i<br />
t j−2 = 1 + +<br />
λ j−1 − λ j λ j−2 − λ j λ j − λ j−1<br />
Now we suppose that the formula holds for n = l, then we have<br />
t l−1 = t l +<br />
j−1<br />
i ∏<br />
λ l−1 − λ j<br />
p=l<br />
λ j − λ p − i<br />
λ j − λ p<br />
=<br />
= λ j − λ j−1 − i λ j − λ j−2 − i<br />
.<br />
λ j − λ j−1 λ j − λ j−2<br />
j−1<br />
∏<br />
p=l−1<br />
λ j − λ p − i<br />
λ j − λ p<br />
,<br />
which proves our assumption. With this formula at h<strong>and</strong> we therefore find<br />
1 +<br />
j−1<br />
∑<br />
i=1<br />
i<br />
λ i − λ j<br />
j−1<br />
∏<br />
p=i+1<br />
j−1<br />
λ j − λ p − i ∏ λ j − λ k − i<br />
=<br />
.<br />
λ j − λ p λ j − λ k<br />
k=1<br />
In the same way one can show that<br />
1 −<br />
j−1<br />
∑<br />
i=1<br />
i<br />
λ i − λ j<br />
j−1<br />
∏<br />
p=i+1<br />
j−1<br />
λ j − λ p + i ∏ λ j − λ k + i<br />
=<br />
.<br />
λ j − λ p λ j − λ k<br />
k=1<br />
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