Matlab problem. Showing capital I and PI in results.

Hi everybody. I've been trying to solve some really huge matrix equations in matlab. But, every time, Matlab shows me, besides number and symbols, capital letter "I" or "PI" in a solution.

I need those equations later in other function for ODE45 solver. Ofcourse, ODE doesn't recognise "I" or "PI".

Here it is some sequance from the result:

1.0*(Kp3*x3 + Kv3*x6 + x11*(cos(- 2*x2 - 2/3*PI*(exp(-2*t^3) - 1)

I define Kp3, x3, Kv3 etc. as symbols, but I didn't mention anywhere "PI" or "I".

Does sombody know what is a problem here? And what should to avoide thise.

Thank you for helping me.