Undefined function or variable t

So I'm very new to matlab and I have been trying to use the ODE45 function, but it keeps coming up with the following error when I try to run my function file. Theres probably something silly im doing wrong.

Undefined function or variable 't'.

Below is the start of the code

function dydt = react1(t,y)
  dydt = zeros(size(t,y));
  p1 = ***;
  p2 = ***;
  p3 = ***;
  p4 = ***;
  p5 = ***;  
  p6 = ***;
  y(1)=G(t);
  y(2)=X(t);
  y(3)=I(t);
  dydt(1) = -(p1+X(t))*G(t)+p1*Gb;
  dydt(2) = -p2*X(t) +p3*(I(t)-Ib);
  dydt(3) = p6*abs(G(t)-p5)-p4*(I(t)-Ib);

Any help would be appricated

[dpb]

Need to see the call to ode45 and the error in context...the problem isn't in the code shown but in the way it is being called that isn't.

Answer 1

[Colton]

You cannot run function files in Matlab. You have to call the function from another script (after you have saved the function, here as 'dydt.m' in your working directory or your path) or call the function from the command window.

You will need to supply some vectors t and y when you call the function.

Answer 2

[Star Strider]

You can call external functions from ODE (and other) functions in MATLAB, but you have to define them as such as function files on your MATLAB path.

It is difficult to follow what you are doing, but if ‘G’, ‘X’, and ‘I’ are functions of time but not defined as such outside your ‘react1’ function, your ‘react1’ function will throw errors.

This could be the correct syntax for your function:

function dydt = react1(t,y)
  dydt = zeros(length(y),1);                          % <- Changed, Must Return A Column Vector
  p1 = ***;
  p2 = ***;
  p3 = ***;
  p4 = ***;
  p5 = ***;  
  p6 = ***;
  G = y(1);
  X = y(2);
  I = y(3);
  dydt(1) = -(p1+X)*G+p1*Gb;
  dydt(2) = -p2*X +p3*(I-Ib);
  dydt(3) = p6*abs(G-p5)-p4*(I-Ib);

NOTE — ‘Gb’ and ‘Ib’ do not appear to be defined in your code, and they are not passed as additional arguments to ‘react1’. Not explicitly defining them or passing them as additional arguments will cause your ‘react1’ code to crash.