Assuming that 'a' is input data and 'x' is the output data, you can use the filter function as shown below
a = 1:5;
num = 1;
den = [1 -1];
x = filter(num,den,a)
for the linear filter equation x(i) - x(i-1) = a(i). However, in your case, it appears like the filter equation is a nonlinear equation. i.e. x(i+1)/x(i) = a(i). So, make sure if your filter equation is correct.
