A general form for a second order linear differential equation is given by a(x)y′′(x)+b(x)y′(x)+c(x)y(x)=f(x).
One can rewrite this equation using operator terminology.
Namely, one first defines the differential operator L=a(x)D2+b(x)D+c(x), where D=ddx.9 juil. 2022
in the unknown y(x).
Equation (1) is first order because the highest derivative that appears in it is a first order derivative.
In the same way, equation (2) is second order as also y appears.
They are both linear, because y, y and y are not squared or cubed etc and their product does not appear.
A general second-order difference equation specifies the state xt at each time t as a function xt = Ft(xt−1,xt−2) of the state at two previous times. of first-order equations that express the vector (xt,yt) ∈ R2 as a function of the vector (xt−1,yt−1) ∈ R2.