[stanking]

thx ngrube, i have tried it. But the result is not good!!
The curve has big oszillation.
Maybe can you check my code?

clc;
clear all;
close all;

Data = load('tg3dn');

E = zeros(1024,1);

L = 1;
N = 1:32;
kx = (2 * pi .* N / L)';
ky = (2 * pi .* N / L)';
kz = (2 * pi .* N / L)';

v = reshape(Data(:,4),32,32,32);
u = reshape(Data(:,5),32,32,32);
w = reshape(Data(:,6),32,32,32);

V = fftn(v);
U = fftn(u);
W = fftn(w);

for i = 1:32,
for j = 1:32,
for m = 1:32,
k = round(sqrt(kx(i)^2 + ky(j)^2 + kz(m)^2));
E(k) = E(k) + abs(V(i,j,m))^2 + abs(U(i,j,m))^2 + abs(W(i,j,m))^2;
end
end
end

index = find(E~=0);
E_index = E(index);
loglog(index,E_index,index,index.^(-5/3));