undefined function or variable x

Why I am getting undefined function or variable x error here?


% Solution of second-order differential equation
% The function diff2(x,y) is created to evaluate the diff. equation
% the name of the m-file is diff2.m
% the function is defined as:
%
function xdot = diff2(t,x)
is = 2;
c = 50e-6; L = 1/32; r = 10;
k1 = 1/c ; % 1/C
k2 = 1/L ; % 1/L
k3 = 1/(r*c); % 1/RC
xdot(1) = k2*x(2);
xdot(2) = k1*is - k1*x(1) - k3*x(2);
% solution of second-order differential equation
% the function diff2(x,y) is created to evaluate
% the differential equation
% the name of m-file is diff2.m
%
% Transient analysis of RLC circuit using ode function
% numerical solution
t0 = 0;
tf = 30*e^-3;
x0 = [0 20]; % Initial conditions
[t,x] = ode23('diff2',t0,tf,x0);
% Second column of matrix x represent capacitor voltage
plot(t,x(:,2))
xlabel('Time, s'), ylabel('Capacitor voltage, V')
text(0.01, 7, 'State Variable Approach')

Answer 1

[Alan Stevens]

Like so (the function must come last in the script):

% solution of second-order differential equation
% the function diff2(x,y) is created to evaluate
% the differential equation
% the name of m-file is diff2.m
%
% Transient analysis of RLC circuit using ode function
% numerical solution
t0 = 0;
tf = 0.03;
x0 = [0 20]; % Initial conditions
[t,x] = ode23(@diff2,[t0 tf],x0);
% Second column of matrix x represent capacitor voltage
plot(t,x(:,2))
xlabel('Time, s'), ylabel('Capacitor voltage, V')
text(0.01, 7, 'State Variable Approach')
%
function xdot = diff2(t,x)
is = 2;
c = 50e-6; L = 1/32; r = 10;
k1 = 1/c ; % 1/C
k2 = 1/L ; % 1/L
k3 = 1/(r*c); % 1/RC
xdot = zeros(2,1);
xdot(1) = k2*x(2);
xdot(2) = k1*is - k1*x(1) - k3*x(2);
end

[AVIJIT NEMO]

Thanks.. It Worked. Are you related to Electrical Field??

[Alan Stevens]

" Are you related to Electrical Field??" ?????

[AVIJIT NEMO]

I mean are you related to Electrical or Electronics Engineering? I have some other matlab problems then i may contact you if you have no problems.

[Alan Stevens]

I'm afraid my knowledge of electricity in general is pretty much limited to Ohm's law!

[Alan Stevens]

Any further contact should be done via the MATLAB forum.

Answer 2

[KSSV]

Save the below code in a file as myfunction.m and run it.

function myfunction()
  % solution of second-order differential equation
% the function diff2(x,y) is created to evaluate
% the differential equation
% the name of m-file is diff2.m
%
% Transient analysis of RLC circuit using ode function
% numerical solution
t0 = 0;
tf = 30*e^-3;
x0 = [0 20]; % Initial conditions
[t,x] = ode23(@diff2,[t0 tf],x0);
% Second column of matrix x represent capacitor voltage
plot(t,x(:,2))
xlabel('Time, s'), ylabel('Capacitor voltage, V')
text(0.01, 7, 'State Variable Approach')

end
% Solution of second-order differential equation
% The function diff2(x,y) is created to evaluate the diff. equation
% the name of the m-file is diff2.m
% the function is defined as:
%
function xdot = diff2(t,x)
is = 2;
c = 50e-6; L = 1/32; r = 10;
k1 = 1/c ; % 1/C
k2 = 1/L ; % 1/L
k3 = 1/(r*c); % 1/RC
xdot(1) = k2*x(2);
xdot(2) = k1*is - k1*x(1) - k3*x(2);
end

Answer 3

[KSSV]

Save the below code in to a file say main.m.

% solution of second-order differential equation
% the function diff2(x,y) is created to evaluate
% the differential equation
% the name of m-file is diff2.m
%
% Transient analysis of RLC circuit using ode function
% numerical solution
t0 = 0;
tf = 30*e^-3;
x0 = [0 20]; % Initial conditions
[t,x] = ode23(@diff2,[t0 tf],x0);
% Second column of matrix x represent capacitor voltage
plot(t,x(:,2))
xlabel('Time, s'), ylabel('Capacitor voltage, V')
text(0.01, 7, 'State Variable Approach')

Save the below code into a function in a file diff2.

% Solution of second-order differential equation
% The function diff2(x,y) is created to evaluate the diff. equation
% the name of the m-file is diff2.m
% the function is defined as:
%
function xdot = diff2(t,x)
is = 2;
c = 50e-6; L = 1/32; r = 10;
k1 = 1/c ; % 1/C
k2 = 1/L ; % 1/L
k3 = 1/(r*c); % 1/RC
xdot(1) = k2*x(2);
xdot(2) = k1*is - k1*x(1) - k3*x(2);
end

After saving the above two files, now run the file in main.m.

[AVIJIT NEMO]

main

Error using odearguments (line 93)

DIFF2 must return a column vector.

Error in ode23 (line 114)

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

Error in main (line 11)

[t,x] = ode23(@diff2,[t0 tf],x0);

Now I am getting this error. Can you please resolve this?