function never used, I dont know why.

I am using code from http://www.chuacircuits.com/matlabsim.php

%----------Chua.m----------

function out = chua(t,in)

x = in(1);

y = in(2);

z = in(3);

alpha = 15.6;

beta = 28;

m0 = -1.143;

m1 = -0.714;

h = m1*x+0.5*(m0-m1)*(abs(x+1)-abs(x-1));

xdot = alpha*(y-x-h);

ydot = x - y+ z;

zdot = -beta*y;

out = [xdot ydot zdot]';

%----------StartChua.m----------

[t,y] = ode45(@chua,[0 100],[0.7 0 0]);

plot3(y(:,1),y(:,2),y(:,3))

grid

end

It confuses me, cause obviously this code was already tested. matlab tells me now i have to put an "end" for the function, even tho the original code doesnt have one, ok I did it.

Then it tells me the function is never used, and [t,y] = ode45(@chua,[0 100],[0.7 0 0]); tells me that the function chua doesnt exist ?

Answer 1

[Star Strider]

In a script, all the function definitions must go at the end of the script:

%----------StartChua.m----------
[t,y] = ode45(@chua,[0 100],[0.7 0 0]);
plot3(y(:,1),y(:,2),y(:,3))
grid

%----------Chua.m----------
function out = chua(t,in)
x = in(1);
y = in(2);
z = in(3);
alpha  = 15.6;
beta   = 28; 
m0     = -1.143;
m1     = -0.714;
h = m1*x+0.5*(m0-m1)*(abs(x+1)-abs(x-1));
xdot = alpha*(y-x-h);
ydot = x - y+ z;
zdot  = -beta*y;
out = [xdot ydot zdot]';
end

That seems to work.

See Create Functions in Files for details.

.

[Martin Mayer]

Thank you for your answer.

I still get the error:

Unrecognized function or variable 'chua'.

Error in odearguments (line 90)

f0 = feval(ode,t0,y0,args{:}); % ODE15I sets args{1} to yp0.

Error in ode45 (line 115)

odearguments(FcnHandlesUsed, solver_name, ode, tspan, y0, options, varargin);

when I use this in command window:

[t,y] = ode45(@chua,[0 100],[0.7 0 0]);

plot3(y(:,1),y(:,2),y(:,3))

grid

[Star Strider]

My pleasure!

It runs as posted in R2021a. It may be necessary to save the ‘chua’ function as ‘chua.m’ on your MATLAB search path with a version/release that does not support functions in files, specifically R2016a and earlier.

.

[Martin Mayer]

I have R2020b. I tried other code before that used functions, it worked, but this one doesn't.

If function has same name as the script, it says Error: File: chua.m Line: 11 Column: 16

Local function name must be different from the script name.

[Star Strider]

Since you have R2020b, if you copy and save the code I posted as a separate script (save it as whatever name you want), it should work just as it worked here.

I have no idea why it doesn’t work for you.

Also, try running the file I just attached. It ran without error when I tried it, and produced the desired result.

.

[Martin Mayer]

Your file worked instant. I dont get it, but thanks. :)

[Star Strider]

My pleasure!

If my Answer helped you solve your problem, please Accept it!

.