please someone solve this error ''Undefined function or variable 'x''.

function  ross
L = [-1.0828 -1.6242;1.2513 1.8770;-0.0020 -0.0029];
master = [-x(2)-x(3);x(1)+0.5*x(2);2+x(3)*x(1)-4*x(3)];
slave = [-x(5)-x(6);x(4)+x(7)*x(5);2+x(6)*x(4)-4*x(6)]-L*y;
thetahat = 2*x(5)*[-0.2308 0.1538]*y;
y =[12*x(1)+2*x(2)+3*x(3)-12*x(4)-x(5)-3*x(6)-2*x(5)*thetahat;7*x(1)+3.5*x(2)+2*x(3)-7*x(4)-2*x(5)-2*x(6)-3*x(5)*thetahat]
x0 = [1 1 1 -5 -5 -5 0];
tspan= [0:0.001:70]; 
options = odeset('RelTol',1e-5,'AbsTol',1e-5);
[t,x]=ode45(@ross,tspan,x0,options)
 function dxdt = ross(t,x)
dxdt = [master;slave;thetahat]
end
end

error is-

Undefined function or variable 'x'.

Error in ross (line 4)

master = [-x(2)-x(3);x(1)+0.5*x(2);2+x(3)*x(1)-4*x(3)];

[Rik]

You don't define x. How do you expect Matlab to know what you mean?

You also have two functions with the same name.

[Meenakshi Tripathi]

sorry! I am a beginner so could you please tell me how to define x?

[Rik]

If you have trouble with Matlab basics you may consider doing the Onramp tutorial (which is provided for free by Mathworks).

Answer 1

[Yongjian Feng]

It seems like lines are all messed up. Do it make more sense to re-arrange them like this:

x0 = [1 1 1 -5 -5 -5 0];
tspan= [0:0.001:70]; 
options = odeset('RelTol',1e-5,'AbsTol',1e-5);
[t,x]=ode45(@ross,tspan,x0,options);
% This looks more like the function. Now x and t are input parameters, and
% they can be used inside the function
function dxdt = ross(t,x)
%function  ross
L = [-1.0828 -1.6242;1.2513 1.8770;-0.0020 -0.0029];
master = [-x(2)-x(3);x(1)+0.5*x(2);2+x(3)*x(1)-4*x(3)];
y =[12*x(1)+2*x(2)+3*x(3)-12*x(4)-x(5)-3*x(6)-2*x(5)*thetahat;7*x(1)+3.5*x(2)+2*x(3)-7*x(4)-2*x(5)-2*x(6)-3*x(5)*thetahat];
slave = [-x(5)-x(6);x(4)+x(7)*x(5);2+x(6)*x(4)-4*x(6)]-L*y;
thetahat = 2*x(5)*[-0.2308 0.1538]*y;
%y =[12*x(1)+2*x(2)+3*x(3)-12*x(4)-x(5)-3*x(6)-2*x(5)*thetahat;7*x(1)+3.5*x(2)+2*x(3)-7*x(4)-2*x(5)-2*x(6)-3*x(5)*thetahat]
% The following lines moved up.
%x0 = [1 1 1 -5 -5 -5 0];
%tspan= [0:0.001:70]; 
%options = odeset('RelTol',1e-5,'AbsTol',1e-5);
%[t,x]=ode45(@ross,tspan,x0,options)
% function dxdt = ross(t,x)
dxdt = [master;slave;thetahat]
%end
end

[Rik]

Actually the relevant defnition of x is in the function signature:

function dxdt = ross(t,x)
%                      ^ here

[Yongjian Feng]

You are right! Modified again.