using sim in matlab armax

Question

I write code below but i find an error that I do not know what it is please help me the error is

Error using idmodel/sim (line 114) The simulation input data must be specified using an iddata object or a double matrix.

Error in Untitled (line 17) y = sim(sys,u);

    clc;
clear all ;
close all;

A = [1 -0.5 0.06];
B = [5 -2]; 
C = [1 -0.2 0.001];
Ts = 1;   %sample time 

sys = idpoly(A,B,C,'Ts',1);

Range = [-1 1];
Band = [0 1];
u = stairs(idinput(100,'prbs',Band,Range));  %form a prbs input

opt1 = simOptions('AddNoise',true);

y = sim(sys ,u,opt1);

iodata = iddata(y,u,Ts);

na = 3;  nb = 2;   nc = 3; nk = 1;
me = armax(iodata,[na,nb,nc,nk]);
compare(iodata,me)

thank you very much

Answer 1

Your input variable u, should be a column vector, but with your code it is a graphics object, use class(u) to check this. If you replace this line

u = stairs(idinput(100,'prbs',Band,Range));  %form a prbs input

with something like this:

u = [zeros(25, 1); ones(25, 1)]; % step input

Then the code no longer crashes.