crack tip functions

Hi,

I am using a X-FEM Matlab code found here http://people.civil.gla.ac.uk/~bordas/xfemMatlab.html"]http://people.civil.gla.ac.uk/~bordas/xfemMatlab.html

In branch.m/branch_node.m (both functions of radius r and angle theta) crack tip fields are defined...and questions arise.

% Functions



f(1) = r2 * st2 ;

f(2) = r2 * ct2;

f(3) = r2 * st2 * ct;

f(4) = r2 * ct2 * ct;