how can i get mean frequency in special rang?

I want to get mean ferequncy in rang f = (0.002 0.55) just this . from this code matlab but i get this eror(Array indices must be positive integers or logical values.)

I do not know how to perform my work to solve this problem

my code matlab is:

for i = 1:1

data1 = load(strcat(strcat('park',num2str(i)),'.ts'));

fft1 = fft(data1);

M2 = abs(fft1.^2./length(data1));

f = (0.8167/2)*(0:(length(data1)-1))/length(data1);

figure,hold on;plot(f,M2(:,13),'r','linewidth',1.5);xlim([0.002 0.55]);

% % extract freq feature

% N = mean(M2(0.002 0.55));

end

Answer 1

[Jonas]

use

mean(M2(f>0.002 & f<0.55))