# Engineering Matlab question

I am an engineering student doing a term project on a slider-crank mechanism, and in getting the differential equation for the slider, I keep getting an error. We are given values for theta = pi( t^2/2 - t^3/2) for 0 <= t <= 1 and theta = 0 for t > 1. I got the equation for the slider as: s(t) = a(1-cos(theta)) + b - sqrt (b^2 - (asin(theta))^2)

I've never taken a matlab course but it is required in this project, and when I try to plug in the equation for the slider, I get the following errors:

>> syms a b t;
>> f = a(1-cos(pi*(t*t/2-t*t*t/2)))+b-sqrt(b*b-(asin(pi*(t*t/2-t*t*t/2))));
Error in MuPAD command: DOUBLE cannot convert the input
expression into a double array.

If the input expression contains a symbolic variable, use the

Error in ==> sym.sym>sym.double at 927

Error in ==> sym.sym>privformatscalar at 2539
x = double(x);

Error in ==> sym.sym>privformat at 2524
s = privformatscalar(x);

Error in ==> sym.sym>sym.subsref at 1364
[inds{k},refs{k}] = privformat(inds{k});

Can anyone help, or is there any way I can define the function for theta to use in the function for the slider, and make it able to differentiate it with respect to time (t)?