See http://www.mathworks.co.uk/matlabcentral/answers/109828-piecewise-functions-using-operator for a way to define an anonymous function in parts.
If each section is polynomial, then see http://www.mathworks.com/help/matlab/ref/mkpp.html and ppval()
In the Symbolic Toolbox, you can use MuPAD's piecewise; see http://www.mathworks.com/help/symbolic/mupad_ref/piecewise.html
Note that there is no direct syntax for this from the MATLAB interface. If you are working from the MATLAB interface, you can use evalin(symengine) or feval(symengine) to construct a piecewise object
