function new_data=change_sampling(old_data,new_x)
% sampling frequency changer
% Author: Yuta Michimura

old_x=old_data(:,1);
old_y=old_data(:,2);
old_dx=old_x(2)-old_x(1);
old_N=length(old_x);
new_N=length(new_x);

if (new_x(1) < old_x(1)) | (old_x(old_N) < new_x(new_N))
    error('ERROR!')
end

new_y=ones(1,new_N)*old_y(old_N);
startkk=1;
for jj=1:new_N
    for kk=startkk:old_N-1
        if (new_x(jj)-old_x(kk))*(new_x(jj)-old_x(kk+1)) < 0
            new_y(jj)=(old_y(kk+1)-old_y(kk))/(old_x(kk+1)-old_x(kk))*(new_x(jj)-old_x(kk))+old_y(kk);
            startkk=kk;
            break
        elseif new_x(jj) == old_x(kk)
            new_y(jj)=old_y(kk);
            startkk=kk;
            break
        end
    end
end

% figure();
% loglog(old_x,old_y,'.',new_x,new_y,'.');
% % % plot(old_x,old_y,'.',new_x,new_y,'.');
% legend('original','resampled');


new_data=[new_x;new_y]';