error in ode45 - must return column vector

This is to simulate the response of a single degree of freedom system.

script

function [ xdot ] = sdof( t, x)

    xdot = zeros(2,3);
    xdot(1) = x(2);
    xdot(2) = -2/3*x(1)-(1/3)*x(2);
end

command window

>> t0 = 0; tf = 20; %-- start and end time

>> x0 = [0 0.25]; %-- initial conditions

>> [t,x] = ode45('sdof',[t0 tf],x0); %-- call ODE45 solver

Error using odearguments (line 90)

SDOF must return a column vector.

Error in ode45 (line 113)

[neq, tspan, ntspan, next, t0, tfinal, tdir, y0, f0, odeArgs, odeFcn, ...

>> plot(t,x);

Undefined function or variable 't'.

Answer 1

[Star Strider]

Replace the preallocation line with:

xdot = zeros(2,1);

and you’re good to go.

Note: in R2014a, I needed to change the ode45 call to:

[t,x] = ode45(@sdof,[t0 tf],x0); %-- call ODE45 solver

Then it worked perfectly.

[Chase]

Perfect thanks so much!!!

[Star Strider]

My pleasure!

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