mu_ss=inverse_inertia(a,diff_a_of_phi,permutations)

function mu_ss=inverse_inertia(a,diff_a_of_phi,permutations)

N=length(a(:,1,1));

if permutations > 0

    trials=length(a(1,1,:))/(2*permutations)+1;

    for i=1:trials

        mu_ss(i)=1/sum(sum(diff_a_of_phi(:,:,i).^2));

    end

    mu_ss(trials+1:2*trials-2)=mu_ss(linspace(trials-1,2,trials-2));

    for i=2:permutations

        mu_ss(end+1:end+1+2*trials-3)=mu_ss(1:2*trials-2);

    end

else

    for i=1:length(a(1,1,:))

        mu_ss(i)=1/sum(sum(diff_a_of_phi(:,:,i).^2));

    end

end