You cannot create a variable as x[j], hoping to create numbered variables. Nor can you ever access the j'th such variable that you just created using xj.
Instead, learn to use cell arrays.
xcell{j} = [xj:xj+1];
You access it using xcell{j}.
I called it xcell, because you already created the variable x as a vector.
Really, what you need to do is to learn MATLAB. There are multiple errors in what you are doing, basic ones that suggest you will benefit from reading the getting started tutorials.
