(ODE45) Unable to perform assignment because the left and right sides have a different number of elements

Hi guys. I have a problem about publishing the ODE45 function and plot.

%% Solving the system of non-linear differential equations
function dx = HW4_matlab(t,x)
dx = zeros(2,1);
dx(1) = exp(-x(1))-x(2)*t;
dx(2) = x(1)*t+cos(x(1)+x(2));
[t,x] = ode45(@HW4_matlab,[1,5],[10,2]);
plot(t,x(:,1),'-b',t,x(:,2),'--r')

When I am going to publish this code, an error shows up:

Unable to perform assignment because the left and right sides have a different number of elements.

Error in HW4_matlab (line 4)

dx(1) = exp(-x(1)) - x(2)*t;

How could I fix it?

Answer 1

[Star Strider]

The code you posted runs for me with out error in R2019b.

The one change I made is to add an end statement to the function:

%% Solving the system of non-linear differential equations
function dx = HW4_matlab(t,x)
dx = zeros(2,1);
dx(1) = exp(-x(1))-x(2)*t;
dx(2) = x(1)*t+cos(x(1)+x(2));
end

[t,x] = ode45(@HW4_matlab,[1,5],[10,2]);
plot(t,x(:,1),'-b',t,x(:,2),'--r')

[Kengchit Lam]

After I added the end statement, there is another type of error:

%% Solving the system of non-linear differential equations
function dx = HW4_matlab(t,x)
dx = zeros(2,1);
dx(1) = exp(-x(1))-x(2)*t;
dx(2) = x(1)*t+cos(x(1)+x(2));
end

[t,x] = ode45(@HW4_matlab,[1,5],[10,2]);
plot(t,x(:,1),'-b',t,x(:,2),'--r')

Error using dbstatus

Error: File: /Users/kennylam/Desktop/CHEN 2001/HW4_matlab.m Line: 8 Column: 1

This statement is not inside any function.

(It follows the END that terminates the definition of the function "HW4_matlab".)

In addition, I am using R2019a

[Star Strider]

Without more information, I have no idea what the problem could be that you are experiencing. As I mentioned, with that one change, your code runs for me withoout error. (I am running it inside a simple function that I use for some Answers problems.)

[Kengchit Lam]

Problem solved! Thank you!

Answer 2

[James Tursa]

It might be simpler to have separate files for this.

Put this code (and only this code) in a file called HW4_matlab.m

%% Solving the system of non-linear differential equations
function dx = HW4_matlab(t,x)
dx = zeros(2,1);
dx(1) = exp(-x(1))-x(2)*t;
dx(2) = x(1)*t+cos(x(1)+x(2));
end

And put this code in a separate file for calling that function

[t,x] = ode45(@HW4_matlab,[1,5],[10,2]);
plot(t,x(:,1),'-b',t,x(:,2),'--r')

[Kengchit Lam]

Problem solved! Thank you James!