is the eigenfunction of the derivative operator, where f0 is a parameter that depends on the boundary conditions. Note that in this case the eigenfunction is itself a function of its associated eigenvalue λ, which can take any real or complex value. In particular, note that for λ = 0 the eigenfunction f(t) is a constant.
Suppose in the example that f(t) is subject to the boundary conditions f(0) = 1 and {displaystyle { frac {df}{dt}}|_{t=0}} {displaystyle { frac {df}{dt}}|_{t=0}} = 2. We then find that