How to calculate gradiant at mesh points in pde toolbox and one more question?

I'm going to calculate grad(u) at mesh points in pde toolbox. Is this a good way? :

 [ux1,uy1] = pdegrad(p,t,u) ;
 ux = pdeprtni(p,t,ux1) ;
 uy = pdeprtni(p,t,uy1) ;

In addition I'd like to know what is meant by "center of triangle" in pde toolbox documentation? Are its coordinates as:

 x_c = (p(1,t(1,j)) + p(1,t(2,j)) + p(1,t(3,j)))/3 ;
 y_c = (p(2,t(1,j)) + p(2,t(2,j)) + p(2,t(3,j)))/3 ;

thanks,

[Mohammad Monfared]

Answer is found!