how to plot a function (partial derivative) in maple using 3D plot

Question

I have the following function

u := proc (x, t) options operator, arrow; 
    50+sum((100*n*Pi*sin(n*Pi)+100*cos(n*Pi)-100)*cos((1/10)*n*Pi*x)*exp(-(1/100)*n^2*Pi^2*t)/(n^2*Pi^2), n = 1 .. 20) 
    end proc;

plot3d(u(x, t), x = 0 .. 10, t = 0 .. 20)

I am trying to plot it in Maple, but is not giving me the right 3D shape.

Answer 1

restart:
u := proc (x, t) options operator, arrow; 
    50+sum((100*n*Pi*sin(n*Pi)+100*cos(n*Pi)-100)*cos((1/10)*n*Pi*x)*exp(-(1/100)*n^2*Pi^2*t)/(n^2*Pi^2), n = 1 .. 20) 
    end proc:

plot3d(u(x, t), x = 0 .. 10, t = 0 .. 20);

plot3d(diff(u(x, t),x), x = 0 .. 10, t = 0 .. 20);