MATLAB never permits indexing at 0. You will need to add 1 to all of your indices. x(0+1) and so on.
Also, MATLAB does not permit transitive assignment. You will need to create two assignment statements.
x(0+1) = 0;
y(0+1) = 0;
for i = 0:k
x(i+1+1) = 1 + y(i+1)-1.4*x(i+1)^2
y(i+1+1) = 0.3*x(i+1)
[x,y]
end
You should ask yourself whether displaying the ever-longer x and y vectors is part of the question, or if you are just intended to return them.
You should also carefully consider how many items long the output vectors are intended to be. for i=0:k does k+1 steps . Are the initial positions (0,0) to be part of the output vectors? If so then is the expected length k exactly, or k+1, or k+2 ?
