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A centered scheme for linear damping
[mD_tD_t u + f(D_{2t}u) + s(u) = F]^n
Written out
m\frac{u^{n+1}-2u^n + u^{n-1}}{\Delta t^2}
+ f(\frac{u^{n+1}-u^{n-1}}{2\Delta t}) + s(u^n) = F^n
Assume f(u') is linear in u'=v :
u^{n+1} = \left(2mu^n + (\frac{b}{2}\Delta t - m)u^{n-1} +
\Delta t^2(F^n - s(u^n))
\right)(m + \frac{b}{2}\Delta t)^{-1}