function blok = blok2D_id(uzly_lok,f_lok)

R_lok = [ uzly_lok(:,2)-uzly_lok(:,1) , uzly_lok(:,3)-uzly_lok(:,1) ];

B = [1/3,1/3,1/3];

blok = f_lok * B' * abs(det(R_lok))/2;
