syms f(t)
g = f( ((x(2)-x(1))*t+(x(1)+x(2)))/2 );
a = w1 * g(x1 + w2 * g(x2) + w3 * g(x3);
Note: this requires about R2011b onward. If you have an earlier version, please indicate which version it is as the capabilities changed a fair bit between R2008a and R2011a.
