Question

PDE \[\delta T / \delta t = D * (\delta ^{2} T / \delta x ^{2})\]
discrete/finite explicit version: \[T _{n}^{i+1} = T _{n}^{i} + \tau (T _{n-1}^{i} + T _{n+1}^{i} - 2T _{n}^{i})\]

How does \[\tau\] depend on D, \[\Delta t\] and \[\Delta x\] ?