could the function expint() use symbol as parameter?

hi, I use expint() in my code, but the parameter is a symbol. matlab give me errors like this:

Error using expint (line 34) Inputs must be floats, namely single or double.

I seach expint in http://www.mathworks.cn/ and find that the expint can accept symbol as input paramter of matlab R2013a. But my matlab version is R2011b.