Markets: A Rigorous Course

M05 · Problem 10 ★★★ Check

Continuous Almgren–Chriss in closed form

For x(t)=Xsinh⁡(κ(T−t))/sinh⁡(κT)x(t) = X\sinh(\kappa(T-t))/\sinh(\kappa T) show that

η∫0Tx˙2dt=ηX2κ2sinh⁡2(κT)(T2+sinh⁡2κT4κ),σ2∫0Tx2dt=σ2X2sinh⁡2(κT)(sinh⁡2κT4κ−T2).\begin{gathered} \eta\int_0^T\dot x^2dt = \frac{\eta X^2\kappa^2}{\sinh^2(\kappa T)}\Big(\frac T2 + \frac{\sinh 2\kappa T}{4\kappa}\Big),\\ \sigma^2\int_0^Tx^2dt = \frac{\sigma^2X^2}{\sinh^2(\kappa T)}\Big(\frac{\sinh2\kappa T}{4\kappa} - \frac T2\Big). \end{gathered}

Find the limits as κ→0\kappa \to 0 (compare with TWAP) and the leading behaviour as κT→∞\kappa T \to \infty. Evaluate for the 5.7 example with λ=10−6\lambda = 10^{-6} and compare with the discrete numbers.

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