- #1
ferret123
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Homework Statement
A dynamical system has a response, y(t), to a driving force, f(t), that satisfies a differential equation involving a third time derivative:
[itex]\frac{d^{3}y}{dt^{3}} = f(t)[/itex]
Obtain the solution to the homogeneous equation, and use this to derive the causal Green's function for this system, G(t;τ). [hint: which order of derivative has a discontinuity at t = τ?]
2. The attempt at a solution
I've obtained a solution to the homogeneous equation [itex]\frac{d^{3}y}{dt^{3}} = 0 [/itex] by integrating 3 times with respect to t giving [itex]y(t) = \frac{1}{2}At^{2} + Bt + C[/itex].
Since I'm looking for a causal Green's function I know for t<τ G(t;τ) = 0.
Taking the advise of the hint I have tried to find which order of derivative has a discontinuity at t=τ. First replacing the driving force, f(t), with a delta function, δ(t-τ), I get
[itex]\frac{d^{3}y}{dt^{3}} = \delta(t-τ)[/itex]
then integrating over the interval [τ-ε, τ+ε] and letting ε tend to 0, I conclude the second derivative changes discontinuously by 1.
Is this correct or have I missed something in determining where the discontinuity lies?
Thanks.