Error in my code

Hi everyone, Im trying to run a dynamic system, but i got some error. if someone know the source of this error please explain it. sys=ss(A,Bc,C,Dc); y=lsim(sys,u,t);

??? Error using ==> DynamicSystem.lsim at 85 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.***

number of rows of U is exactly the same as T. I dont know what does Input Channels mean?

Your help will be apprecuated

[Azzi Abdelmalek]

Can you post the values of A,Bc,C,Dc,u and t

[Brwa]

Hi Azzi, its abig matrix, so please look at my answer i have explained the question in more detail

Thanks

Answer 1

[Azzi Abdelmalek]

%Dc is (9,2), which means that your system has 2 inputs ans 9 outputs
the input u  should be (100,2)
and t (100,1)

Answer 2

[Walter Roberson]

If I recall correctly (dubious), the number of input channels is set when you construct "sys", so you have to match one of the sizes with that.

Answer 3

[Brwa]

thanks for your answers and comments. actually Im trying to solve a state space sytem which is

x'=Ax + Bc*u
y =Cx + Dc*u
sys=ss(A,Bc,C,Dc);  
y=lsim(sys,u,t);

where

A (6,6) matrix
Bc is (6,2)
C is (9,6)
Dc is (9,2).
u is (100,1) vector
t is (100,1) vector

I hope someone can help me, I appreciate all your helps

Answer 4

[Brwa]

Thanks Mr. Azzi Abdelmalek. yes, you are right.

Answer 5

[Brwa]

I have posted another question, please take alook if you can answer me. I appreciate your help

http://www.mathworks.com/matlabcentral/answers/76363-changing-position-of-numbers-in-a-vector

Answer 6

[Edward Desmond]

% Given parameters

Pr = 2.65; % Average density (g/cm³)

Kr = 7.75e-3; % Thermal conductivity (cal/cm s °C)

Cp = 0.197; % Heat capacity (cal/g °C)

Tinit = 323; % Initial temperature (K)

Tapplied = 423; % Applied temperature (K)

tmax = 2; % Simulation time (years)

reservoirExtent = 75; % Reservoir extent (m)

% Convert units

Kr = Kr * 418.4; % Convert thermal conductivity to (W/m K)

Cp = Cp * 4.184; % Convert heat capacity to (J/kg K)

% Discretization parameters

nr = 100; % Number of radial grid points

dr = reservoirExtent / (nr - 1); % Radial grid spacing

% Time discretization parameters

dt = 0.01; % Time step size

nt = round(tmax * 365.25 * 24 * 60 * 60 / dt); % Number of time steps

% Initialize temperature matrix

T = zeros(nr, nt+1);

T(:, 1) = Tinit; % Set initial temperature

% Perform time-stepping

for i = 1:nt

% Perform radial discretization

for j = 2:nr-1

% Calculate thermal diffusivity

alpha = Kr / (Cp * Pr);

% Calculate radial derivatives

dT_dr = (T(j+1, i) - T(j-1, i)) / (2 * dr);

d2T_dr2 = (T(j+1, i) - 2 * T(j, i) + T(j-1, i)) / (dr^2);

% Update temperature using finite difference method

T(j, i+1) = T(j, i) + alpha * dt * (d2T_dr2 + (1 / j) * dT_dr);

end

% Apply boundary conditions

T(1, i+1) = T(2, i+1); % Symmetry boundary condition

T(nr, i+1) = T(nr-1, i+1) + dr * (Tapplied - T(nr, i+1)); % Heat conduction at reservoir boundary

end

% (1) Reservoir temperature at a distance of 20 m after 2 years

distance = 20;

index = round(distance / dr) + 1; % Add 1 to account for MATLAB indexing

temperature = T(index, end);

% (2) Energy needed to heat the reservoir at 20 m

mass = Pr * reservoirExtent * pi * dr^2;

energy = mass * Cp * (Tapplied - Tinit);

% (3) Viscosity change at 20 m (using a hypothetical correlation)

viscosityInitial = 10; % Initial viscosity (cP)

correlationConstant = 0.5;

viscosityChange = correlationConstant * (temperature - Tinit);

% Plotting temperature profile

r = linspace(0, reservoirExtent, nr);

figure;

plot(r, T(:, end));

xlabel('Radial Distance (m)');

ylabel('Temperature (K)');

title('Temperature Profile in the Reservoir');

% Displaying the results

fprintf('Reservoir temperature at 20 m after 2 years: %.2f K\n', temperature);

fprintf('Energy needed to heat the reservoir at 20 m: %.2f J\n', energy);

fprintf('Viscosity change at 20 m: %.2f cP\n', viscosityChange);