I keep getting ode45 (line 115) and odearguments (line 90) errors

This code was given to me by my professor for a dynamics project.

function [t,x,fN]=lab2(x0,f0,om)

m = 2;

L = 0.6;

NPERD = 250;

npt_PERD = 200;

dt = 2*pi/om/npt_PERD;

tspan = dt*(1:NPERD*npt_PERD);

N = length(tspan);

opt = odeset('RelTol',1e-10,'AbsTol',1e-9);

[t,x] = ode45(@bar,tspan,x0,opt,m,L,f0,om);

function G = bar(t,x,m,L,f0,om)

% x(1): position of wheel (point A)

% x(2): velocity of wheel

% x(3): angle of the bar

% x(4): angular velocity of the bar

G(1,1)=x(2);

G(3,1)=x(4);

A = [m 0.5*m*L*cos(x(3));0.5*m*L*cos(x(3)) m*L^2/3];

rhs(1,1)= 0.5*m*L*(x(4))^2*sin(x(3))+f0*cos(om*t); % enter p function on the RHS of EOM

rhs(2,1)= -0.5*m*g*L*sin(x(3)); % enter q function on the RHS of EOM

G([2 4],1)=A\rhs;

I was only required to determine the two equations for rhs(1,1) and rhs(2,1) and plug them into the code. However, I'm getting several errors and I just don't understand much of what he's written for the program. These are the errors I'm getting:

>> lab2(0,5,25*pi)

Index exceeds array bounds.

Error in lab2>bar (line 19)

G(1,1)=x(2);

Error in odearguments (line 90)

f0 = feval(ode,t0,y0,args{:}); % ODE15I sets args{1} to yp0.

Error in ode45 (line 115)

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

Error in lab2 (line 11)

[t,x] = ode45(@bar,tspan,x0,opt,m,L,f0,om);

What am I doing wrong?

Answer 1

[Steven Lord]

Your x0 input to lab2 is a scalar so when you passed that into ode45 that tells ode45 that you have one initial condition. Because of that, you're solving a system of one ODE. There is no second element of the x vector with which ode45 calls your bar function, so when you try to ask for the value of that second element MATLAB correctly throws an error.

Your wheel starts off at position 0 at time 0. What's its initial velocity at that time? What are the initial angle and angular velocity of the bar at that time? Specify those in x0.

[Steven Lord]

It depends on what type of plot you want. The plot function is the most straightforward, giving you a 2-D line plot, but if you want something different click on the Plots tab in the Toolstrip and expand the PLOTS section using the small downward-pointing triangle.

If you select variables in the Workspace window then when you expand the PLOTS section it will show just plot types that you can create using those variables. See if one looks like the plot you want to create, then click on it. MATLAB will "type" the command in the Command Window and create the selected plot.

If you haven't selected any data, you can't insert the command into the Command Window. But this will show you the name of the function to create that type of plot so you can read more about it in the documentation and perhaps adapt one of the documentation examples.

For the angular data, a polarplot may be appropriate.

[Daniel]

I was able to figure it out, it was simple enough with the plot function. Thanks again

[Steven Lord]

There was a comment by Daniel (since deleted) between my answer and my comment remarking that I'd correctly identified the problem and asking how to plot some aspects of the solution.

Daniel, please don't delete comments when doing so would make the flow of the conversation discontinuous as in this case (my comment talking about plots seems a non sequiter without the comment.)

[Daniel]

My apologies. I had deleted it since I was able to get the plots. I didn't refresh the page first to see if there was a response before doing so. Won't happen again