We build an ARX model, where [na nk nb] = [ 3 2 1] and with 8 inputs and 6 outputs. If we use this model to calculate the outputs for k+1 with sim.m and predic.m functions, we get pretty different results. I would expect that for k+1 the results of these two functions would be the same (and for further steps, i.e. k+2,k+3,... there would be a difference).
From where comes the difference between the sim and predict functons in calculating k+1 step?