train dynamics undefined variable and ode problem

hello,

i need help about ode23 and subfunction topic

function xdot=train(t,x) alfa=0.3; beta=0.13; gama=0.16; Ua=1; Ub=2; xdot=[x(2);((2/pi)*(atan((x-4)/0.05)+atan((x-2)/0.05))-alfa-beta*abs(x(2))-gama*(x(2)^2)+Ua-Ub)];

end

and the plot function

[t,x]=ode23('train',[0,0.1],[0;0]); subplot(2,1,1);plot(t,x(:,1)) subplot(2,1,2); plot(t,x(:,2))

qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq

and the error is

??? Error using ==> odearguments at 116 TRAIN returns a vector of length 3, but the length of initial conditions vector is 2. The vector returned by TRAIN and the initial conditions vector must have the same number of elements.

Error in ==> ode23 at 172 [neq, tspan, ntspan, next, t0, tfinal, tdir, y0, f0, odeArgs, odeFcn, ...

Error in ==> main1 at 1 [t,x]=ode23('train',[0,0.1],[0;0]);

THANKS FOR YOUR HELP.....

[Walter Roberson]

As an editor on this site, I normally leave terms such as "urgent" in place for tracking purposes. Your title term of "Emergency" was beyond my tolerance and I have removed it.

If you post that something is an "emergency" then you should be able to document that there was a literal and immediate risk of loss of life, or at least of serious and literal risk of damage to health (e.g., a broken leg.) If emergency officials such as ambulance or fire department or police or doctors did not get involved, then it was probably NOT an emergency.

[sarngon]

sorrry

Answer 1

[Walter Roberson]

Your expression for xdot has two atan() calls with arguments that are expressions in x -- but x is a vector, so you get out a vector result the same length as x... but you also put x(2) at the front of that vector, resulting in a vector of length 3.

[sarngon]

Hi can u help me pls i added a message to my ouestion

thanks

Answer 2

[sarngon]

ok i change the matrix variable name as k(2)and kdot but now the prog gives such a error

codes function kdot=train(t,x) alfa=0.3; beta=0.13; gama=0.16; Ua=1; Ub=2; kdot=[k(2);(2/pi)*(atan((x-4)/0.05)+atan((x-2)/0.05))-(alfa+beta*abs(k(2))+gama*(k(2)^2))+Ua-Ub];

end

and the error line

??? Undefined function or method 'k' for input arguments of type 'double'.

Error in ==> train at 7 kdot=[k(2);(2/pi)*(atan((x-4)/0.05)+atan((x-2)/0.05))-(alfa+beta*abs(k(2))+gama*(k(2)^2))+Ua-Ub];

thanks..

[Walter Roberson]

You have no function or variable named "k" so k(2) has no meaning.

Renaming to k and kdot is not going to solve your problem that you are trying to output three values in a context that only expects two values. You still have (x-4) and (x-2) in your calculations and since x is a vector, (x-4) and (x-2) will be vectors the same size as x. Please re-check your original equations: you might find that you want (x(1)-4) for example.

[sarngon]

yeah i found thanks for your help.. there i must use atan(x(1)) instead of atan(x)

[Walter Roberson]

The Question is solved then?

Answer 3

[devalaraju venkata naga amulya]

Hello I want to know that how to know the ode's in a vehicle train model. we can calculate manually if the degrees of freedom is small like 5,10 . but what is it is lie 41DOF and more than that . is there any possible approach in matlab to directly code a script and get to know the equations for the system by coding anything in matlab. kindly help and suggest anything in this regard.

thank you in advance