Not enough input arguments

function xdot = OD(t,x)
global A B C Da K
Aa=A+(B*K*C);
Ba=B*Da;
u=K*x;
xdot=(Aa*x)+(Ba*u);
end

When running this code it show error in the line u=K*x; as not enough inputs. Here A,B,C,Da,K are all 2x2 matrix.

[Vashist Hegde]

The code looks fine. The error does not seem to be for line:5

Are you sure that while running this function, you are giving t,x as arguments?

[Sargondjani]

Look at the workspace when you get the error (with "dbstop if error"). Are K and x defined?

[Rik]

Did you run this function with the green button (or with the f5 hotkey)?

[Reeshabh Kumar Ranjan]

Did you save the file before running it again?

[Stephen23]

Rather than using global variables you should parameterize the function:

https://www.mathworks.com/help/matlab/math/parameterizing-functions.html

[Gopika R]

@Vashist Hedge: Yes, the arguments are t and x.

[Gopika R]

@Rik: I ran it with the play button, the green one.

[Walter Roberson]

When you use the green run button, then where are you expecting that MATLAB will look for the values of t and x to use inside the routine?

Answer 1

[Ameer Hamza]

It seems that you are trying to solve a matrix differential equation. If you are using ode45, one possible way this error can occur if you call it like this

ode45(@(t,x) OD, [0 10], [1; -1; 0; 0])

The correct syntax is

ode45(@(t,x) OD(t,x), [0 10], [1; -1; 0; 0]) % or
ode45(@OD, [0 10], [1; -1; 0; 0])

The following shows working code with random values for matrices

global A B C Da K

A = rand(4);
B = rand(4);
C = rand(4);
Da = rand(4);
K = rand(4);

ode45(@(t,x) OD, [0 10], [1; -1; 0; 0])

function xdot = OD(t,x)
global A B C Da K
Aa=A+(B*K*C);
Ba=B*Da;
u=K*x;
xdot=(Aa*x)+(Ba*u);
end

Also, using global variables is not a good coding practice. Following shows how to pass these matrices to function OD without using global

A = rand(4);
B = rand(4);
C = rand(4);
Da = rand(4);
K = rand(4);

ode45(@(t,x) OD(t,x,A,B,C,Da,K), [0 10], [1; -1; 0; 0])

function xdot = OD(t,x,A,B,C,Da,K)
Aa=A+(B*K*C);
Ba=B*Da;
u=K*x;
xdot=(Aa*x)+(Ba*u);
end

[Gopika R]

OK. Thank you. I will try with this.