function []=spectrum(t,u)
m=max(size(t));
m2=floor(m./2);
fu=fft2(u);
fun=fu(2:m2);
power=abs(fun).^2;
plog=log(1+power);
plogsmooth=smooth(plog);
time=t(m);
fmin=1./time;
fmax=0.5./(t(2)-t(1));
n=max(size(fun));
f=fmin+(fmax-fmin).*[0:(n-1)]./(n-1);
h=plot(f,plogsmooth);
set(h,'linewidth',3)