Why do I receive error stating that function needs to appear at the end of the file? MATLAB Differential Equations Help

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May someone help me figure out why I keep getting the error at the end of this message?
global alpha
global beta
% Y = [x(t) y(t)], Y(1) = x(t), Y(2) = y(t)
function [dx_dt dy_dt] = odefun(t, Y)
x = Y(1); y = Y(2);
global alpha
global beta
dx_dt = beta * (1 - x - y) * x - alpha * x;
dy_dt = alpha * x;
end
alpha = 0.1;
beta = 0.1;
for x0 = [0:0.05:0.5]
alpha = 0.1
beta = 0.1
fig = figure;
[t_array, Y_array] = ode45(odefun, [0:200], [x0 0]);
plot(t_array, Y_array)
end
alpha = 0.05;
beta = 0.2;
for x0 = [0:0.05:0.5]
fig = figure;
[t_array, Y_array] = ode45(@odefun, [0:200], [x0 0]);
plot(t_array, Y_array)
end
Error: File: projectF.m Line: 11 Column: 1
Function definitions in a script must appear at the end of the file.
Move all statements after the "odefun" function definition to before the first local function
definition.

Answers (1)

Walter Roberson
Walter Roberson on 30 Nov 2023
It is just a Fact Of Life with MATLAB. You have some non-function statements, then you define a function, then you end the function, then you have more non-function statements. MATLAB considers your script (the original non-function statements) to have ended as soon as the first function definition appeared, and doesn't know what to do with the non-function statements after the function definition. Just move the function definition to the end.
global alpha
global beta
% Y = [x(t) y(t)], Y(1) = x(t), Y(2) = y(t)
alpha = 0.1;
beta = 0.1;
for x0 = [0:0.05:0.5]
alpha = 0.1
beta = 0.1
fig = figure;
[t_array, Y_array] = ode45(odefun, [0:200], [x0 0]);
plot(t_array, Y_array)
end
alpha = 0.1000
beta = 0.1000
Not enough input arguments.

Error in solution>odefun (line 24)
x = Y(1); y = Y(2);
alpha = 0.05;
beta = 0.2;
for x0 = [0:0.05:0.5]
fig = figure;
[t_array, Y_array] = ode45(@odefun, [0:200], [x0 0]);
plot(t_array, Y_array)
end
function [dx_dt dy_dt] = odefun(t, Y)
x = Y(1); y = Y(2);
global alpha
global beta
dx_dt = beta * (1 - x - y) * x - alpha * x;
dy_dt = alpha * x;
end
  3 Comments
Walter Roberson
Walter Roberson on 30 Nov 2023
You cannot return multiple derivatives on the left side of an ode function. You need to return a column vector as the single output of the ode function. (There might potentially be other outputs as well, depending on options you have configured.)
global alpha
global beta
% Y = [x(t) y(t)], Y(1) = x(t), Y(2) = y(t)
alpha = 0.1;
beta = 0.1;
for x0 = [0:0.05:0.5]
alpha = 0.1
beta = 0.1
fig = figure;
[t_array, Y_array] = ode45(@odefun, [0:200], [x0 0]);
plot(t_array, Y_array)
end
alpha = 0.1000
beta = 0.1000
alpha = 0.1000
beta = 0.1000
alpha = 0.1000
beta = 0.1000
alpha = 0.1000
beta = 0.1000
alpha = 0.1000
beta = 0.1000
alpha = 0.1000
beta = 0.1000
alpha = 0.1000
beta = 0.1000
alpha = 0.1000
beta = 0.1000
alpha = 0.1000
beta = 0.1000
alpha = 0.1000
beta = 0.1000
alpha = 0.1000
beta = 0.1000
alpha = 0.05;
beta = 0.2;
for x0 = [0:0.05:0.5]
fig = figure;
[t_array, Y_array] = ode45(@odefun, [0:200], [x0 0]);
plot(t_array, Y_array)
end
function [dxdy_dt] = odefun(t, Y)
x = Y(1); y = Y(2);
global alpha
global beta
dx_dt = beta * (1 - x - y) * x - alpha * x;
dy_dt = alpha * x;
dxdy_dt(1,1) = dx_dt;
dxdy_dt(2,1) = dy_dt;
end

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