Ratio of data values

I need to have a ratio for my errors. so the first ratio in the row should be 0, then the next one should be .080081/0.689885 to get the ratio for row 2, and the the next row .008140/.080081 and so on for the next value.

clc;
clear all;
format long

f=@(t,y)2*y;

a=0; %lower limit
b=0.5; %upper limit

disp('----------------------------------------------------------------------------') %display
disp( ' N             aprroximation               Erorr                      Ratio               ')
disp('----------------------------------------------------------------------------')%display
N=5; % number of intervals
while(N<=5000)
h=(b-a)/N; %step length
t=a:h:b;
y_eu(1)=3; % intial conditon
%Euler formula
for i=1:N
    y_eu(i+1)=y_eu(i)+h*f(t(i),y_eu(i));
end

%Exact solution
for i=1:N+1
     y_ex(i)=3*exp(2*t(i));
end
erorr=(abs(y_eu(end)-y_ex(end)));
ratio=1;
fprintf('%0.4d \t%20f \t%20f\t%20f\n',N,y_eu(end),erorr,ratio)%display of graph
N=N*10;
end
plot(t,y_eu)
hold on
plot(t,y_ex,'r')