Demo for example 9.6.2, plucked string animationwith(plots):a:=2; b:=1; L:=10;A(n) := 4*b*L/(n*Pi)^2 * sin(n*Pi/2);y := (x,t,N) -> sum( A(n)*cos(n*Pi*a*t/L) * sin(n*Pi*x/L) , n=1..N);animate(plot,[y(x,t,30),x=0..L],t=0..20);Demo for D'Alembert's solutionf := x -> piecewise(4.5 <= x and x < 5, 2*(x-4.5), 5 <= x and x <= 5.5, 2*(5.5-x));animate(plot, [ 0.5* (f(x-a*t) + f(x+a*t)),x=0..10],t=0..2);