>    #Vibration of stretched membrane with fixed edges, Ex 1,page 159
u:=(x,y,t)->sum(sum(64/(Pi^6*(2*k+1)^3*(2*l+1)^3)*sin((2*k+1)*Pi*x)*sin((2*l+1
)*Pi*y)*cos(sqrt((2*k+1)^2+(2*l+1)^2)*t), l=0..5), k=0..5);  with(plots):plot3d(u(x,y,2), x=0..1,y=0..1,title="Ex. 1, u(x,y,2)");

u := proc (x, y, t) options operator, arrow; sum(sum(64/Pi^6/(2*k+1)^3/(2*l+1)^3*sin((2*k+1)*Pi*x)*sin((2*l+1)*Pi*y)*cos(sqrt((2*k+1)^2+(2*l+1)^2)*t),l = 0 .. 5),k = 0 .. 5) end proc
u := proc (x, y, t) options operator, arrow; sum(sum(64/Pi^6/(2*k+1)^3/(2*l+1)^3*sin((2*k+1)*Pi*x)*sin((2*l+1)*Pi*y)*cos(sqrt((2*k+1)^2+(2*l+1)^2)*t),l = 0 .. 5),k = 0 .. 5) end proc

[Maple Plot]

>    with(plots): animate3d(u(x,y,t),x=0..1,y=0..1,t=0..4*Pi,frames=30);

[Maple Plot]

>