Matlab ode15s error: subscript indices must either be real positive integers or logicals.

Hello,

I have the following differential equation to be solved:

 g1=0.988122979147950;
g2=0.644414268521746;
beta1=14.6523799554469;
beta2=-10.9849944881532;
beta3=411.648214174951;
g=227.598238564395;
n=1.56153644411635;
global spxdot;
shapeFunc=@(t,z)1-g1.*exp((-z.*abs(ppval(spxdot,t))/g2).^2).*ppval(spxdot,t).*(1-(beta1.*(sign(ppval(spxdot,t).*z)+beta2.*sign(ppval(spxdot,t)))+beta3.*sign(z)+ g).*(abs(z).^n));
trange=linspace(1,2401,2401)/1000;%converting to seconds
z0=0;%value of z at time t=0 
[T,z1]=ode15s(shapeFunc,trange,z0);

But I am getting the following error:

Subscript indices must either be real positive integers or logicals.
Error in
differential>@(t,z)1-g1.*exp((-z.*abs(ppval(spxdot,t))/g2).^2).*ppval(spxdot,t).*(1-(beta1.*(sign(ppval(spxdot,t).*z)+beta2.*sign(ppval(spxdot,t)))+beta3.*sign(z)+g).*(abs(z).^n))
Error in odearguments (line 87)
f0 = feval(ode,t0,y0,args{:});   % ODE15I sets args{1} to yp0.
Error in ode15s (line 150)
  odearguments(FcnHandlesUsed, solver_name, ode, tspan, y0, options, varargin);
Error in differential (line 27)
[T,z1]=ode15s(shapeFunc,trange,z0);

Would somebody point out where I am doing the mistake? I double-checked the parens and operators but found nothing wrong.

Thanks,

[Torsten]

Did you try calling your function "shapeFunc" with a specified argument for t and z, e.g.

t=0.5;
z=20;
result = shapeFunc(t,z)

Does it work as expected ?

Best wishes

Torsten.

[Chinmay Sharma]

No, it doesn't.

Meaning that the error is in the function?

[Torsten]

Yes.

See if you can really evaluate the structure:

t = 0.5;
result = ppval(spxdot,t)

Best wishes

Torsten.

[Chinmay Sharma]

I figured it out. I made a very silly mistake.

I had another experiment data struct named 'exp' in the workspace while running the code. Matlab assumed exp to be a struct rather than a function. Once that was removed, it worked fine.

Thanks for the help, and sorry for the trouble!