I want to use 'u' as zero matrix in order to simulate the matrix but I am receiving the following error, which is mentioned below the code. what's the possible solution?

clear all 
close all
clc

s = -14.5 

A = [-3, 5, -7, 0; 0.5, -1.5, 0.5, -7.5; -5, 0, -3, 0; -0.5, -5, 0, -7];

B = [1, 0; 0, -1; -2, 0; 0, 1];

C = [1, 0, 0, 0; 0, -1, 0, 0];

D = [-1, 0; 2, 0];

sys = ss(A,B,C,D);
M = (s*eye(4,4) - A);
P = [ M, -B; C, D]
k = rank(P)
d = det(P)
uM = null(P,'r')
sys2 = tf( sys );
t = 0:0.1:10;
u = zeros([4 1]) %this is the matrix because of which I am receiving error
[y,t] = lsim(sys2 ,u , t)
size(y)

error:-

Error using DynamicSystem/lsim (line 84)

When simulating the response to a specific input signal, the input

data U must be a matrix with as many rows as samples in the time

vector T, and as many columns as input channels.

Error in antiresonance_part_two (line 44)

[y,t] = lsim(sys2 ,u , t)

[Walter Roberson]

What is the difference between this and https://www.mathworks.com/matlabcentral/answers/744507-how-to-simulate-using-lsim-command-i-am-receiving-error-because-of-variable-t-time?s_tid=srchtitle which you already received an answer for?

[Virendra Kowale]

Earlier question was not specific and was kind of wrong code because earlier i used calculated initial state as input u, which i should not have done

[Virendra Kowale]

clear all

close all

clc

s = -14.5

A = [-3, 5, -7, 0; 0.5, -1.5, 0.5, -7.5; -5, 0, -3, 0; -0.5, -5, 0, -7];

B = [1, 0; 0, -1; -2, 0; 0, 1];

C = [1, 0, 0, 0; 0, -1, 0, 0];

D = [-1, 0; 2, 0];

sys = ss(A,B,C,D);

M = (s*eye(4,4) - A);

P = [ M, -B; C, D]

k = rank(P)

uM = null(P,'r')

I = transpose(uM)

%sys2 = tf( sys );

t = linspace(0, 2.5, 10).';

x_zero = transpose([0,0,0,-0.1333])

u = x_zero.*exp(-14.5*t)

x0= initial(sys,x_zero)

[y,t] = lsim(sys ,u , t)

error that I am receiving:-

Matrix dimensions must agree.

Error in antiresonance_part_two (line 36)

u = x_zero.*-exp(-14.5*t)

[Star Strider]

See my Answer to wheat is apparently a cuplicate of this Question how to simulate using lsim command I am receiving error because of variable 't'(time).

Answer 1

[Walter Roberson]

When simulating the response to a specific input signal, the input

data U must be a matrix with as many rows as samples in the time

vector T, and as many columns as input channels.

Let us look at what you have

t = 0:0.1:10;
size(t)

ans = 1×2

1 101

t has 101 samples. According to the error message (which we will assume to be correct as it says the same thing as the documentation for lsim says), as many rows as samples in the time u must have 101 rows as well.

u = zeros([4 1]) %this is the matrix because of which I am receiving error

That is clearly 1 column. Does it satisfy as many columns as input channels ?

C = [1, 0, 0, 0; 0, -1, 0, 0];

2 rows for C -> two input channels. So u must have two columns because the system has two input channels.

Therefore, you would be able to get something to run if you used

u = zeros(length(y), 2);

Would it be a meaningful run? Probably not. Row K of u should be the list of inputs corresponding to time t(K), so using zeros() like that is telling lsim() that the inputs are zero at every time step. Not impossible, but not likely.

[Virendra Kowale]

yes u r right I didn't mention but I was trying something like that. So that input u corresponds to time t

u = zeros(length(t), 2);

C is output matrix, so I think number columns should be dependent upon B matrix.

Please correct me if I am wrong

[Walter Roberson]

You are right, the number of inputs is the number of columns of B, not the number of rows of C. It happened to be the same in this case.