# train dynamics undefined variable and ode problem

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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))

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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.....

### Answers (3)

Walter Roberson
on 25 Jan 2012

devalaraju venkata naga amulya
on 23 Feb 2021

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

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