How do I graph a summation over an interval?

I have to plot this on the interval x E [-1,1] and x E [-0.1,0.1] for N=10. Can anyone help? I've tried symsum, but it doesn't work.

[Torsten]

The good old Weierstrass function:

https://en.wikipedia.org/wiki/Weierstrass_function

Answer 1

[Matt J]

n=(0:10).';

fcn=@(x)sum( (2/3).^n .* cos(9.^n.*(pi.*x))  );

fplot(fcn,[-1,1]/10)