diff_a_of_phi=a_prime_of_phi(a);

function diff_a_of_phi=a_prime_of_phi(a);

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

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

s_values=linspace(0,2*pi,trials+1);

s_points=s_values(1:length(s_values)-1);

for i=1:N

    for j=1:3

        ppfun=ppcreate(s_points,a(i,j,:),'spline');

        ppfun_prime=ppcreate(ppfun,'diff');

        diff_a_of_phi(i,j,:)=permute(ppfun_prime(s_points),[3 1 2]);

    end

end