index out of bounds because of numel????

Hi,

I am having Problems with the below function and script.

function [ xdot ] = aq_1( t,x )
global m c k y
xdot(1) = x(2);
xdot(2) = (1/m)*((2*k*y)-c*x(2)-2*k*x(1));
xdot=[xdot(1);xdot(2)];
end

global m c k y
m=500*9.81;%Mass of object M = 500kg
c=400; %Dampening coefficient of shock absorber c = 400Ns/m
k=5; %Spring stiffness of each spring k = 5kN/m
tspan=[0:0.01:10];
b=0.05;%bump in metres
v=11.11;%velocity v = 40km/h or 11.11m/s
s=v*tspan;
w=2*pi/2;
y = b*sin(w*s);
[t,x]=ode45('aq_1',tspan,0);
plot(t,x(:,2))

This is the series of warnings I get below. I can't get my head around the first one of being out of bounds and can't find what a numel is.

I know it is a bit of an ask but I would appreciate the help.

Thanks

Attempted to access x(2); index out of bounds because
numel(x)=1.

Error in aq_1 (line 3)
xdot(1) = x(2);

 Error in odearguments (line 88)
f0 = feval(ode,t0,y0,args{:});   % ODE15I sets args{1}
to yp0.

Error in ode45 (line 114)
[neq, tspan, ntspan, next, t0, tfinal, tdir, y0, f0,
odeArgs, odeFcn, ...

Answer 1

[Image Analyst]

How did you call this function? Did you pass it an "x" with more than one element? Evidently not. Put this line as the first line in your function:

whos x

then look at this link: http://blogs.mathworks.com/videos/2012/07/03/debugging-in-matlab/ which will help you more than you can imagine. It will give you great power at solving things like this.

[Image Analyst]

Forgot to refer you to this link also: http://www.mathworks.com/matlabcentral/answers/13205-tutorial-how-to-format-your-question-with-markup

[Martin]

thanks for the quick response