Error in script - 'undefined function'

Hi all!

I'm new to Matlab so am encountering many problems. Here, I have written a script laying out the variables of an ODE which I will later attempt to solve using ode45. However, when I try to call the function it gives me this messgae. (Context: Xo and Xi are the volumes of water in the outer and inner layer of a leaf respectively, where Xo + Xi = 1).

I have tried to figure out the problem using online help but to no avail so any help would be greatly appreciated!

Answer 1

[madhan ravi]

Xi must be a numerical value , in your case you didn't define it which causes error

[Daniella Crispi]

Thanks for your response!

My ODEs though are in terms of Xo and Xi and all the other variable stated (a, b, Uh etc):

Do you have any idea how I could go about solving these? (Am I on the right track with creating a script that defines the variables?)

Thanks

[madhan ravi]

I have no idea what you did but I solved it in terms as function of t

t=[0 1]; %time interval
y0=[0 0]  %initial conditions
[t,x]=ode45(@myod,t,y0);
plot(t,x)
 
function dxdt = myod(t,x)
%x(1)->Xo
%x(2)->Xi
a=3600;
b=3600;
uh=3; %fake data
ua=2; %fake data
uc=7; %fake data
mu=7; %fake data
x(1)=1-x(2);
dxdt=zeros(2,1);
dxdt(1)=(a*x(1).^2)./(x(1).^2+x(2).^2)+uh+ua-uc-mu.*x(1);
dxdt(2)=(a*x(2).^2)./(x(1).^2+x(2).^2)-uh-ua+uc-mu.*x(2);
end

[Daniella Crispi]

Impressive! Thanks very much, I'll give that a go! Does all of that go in the command window or do I need to create a file in the editor? (Also where are you getting the values or 3, 2 and 7 for the u terms?)

[madhan ravi]

As mentioned earlier the values have to be numerical, you can copy my answer and save it as a script file and then run it

[Daniella Crispi]

Their values are dependent on Xo and Xi though.

I will send you the article I have taken all of this from as I haven't explained the context! Here you can see all their parameter values and their graphs of results (which I am trying to replicate - to not much success as you can see!).

https://www.tandfonline.com/doi/pdf/10.4161/psb.5.8.12136?needAccess=true - the main stuff of on pages 7-9.

[Stephen23]

"Their values are dependent on Xo and Xi though."

Then parameterize the function using either nested functions or an anonymous function:

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

[Daniella Crispi]

I'll check that out, thanks!

[Daniella Crispi]

I've run into another problem which I can't work out - I'm trying to work through the example on the page you sent me. However when I try to call the saved function in the command window I get this message - any ideas?

[Daniella Crispi]

Oops - just realised the values I typed in the command line are slightly different to those in the example. (However I retyped it correctly and the same message shows).