function	small = Gamma_rep(big)

%Gamma_rep= Gamma representation
%big is 4x4 matrix
%small is 3x3 matrix
%Finds small_{ij} = eye(3)*trace(big)/4 +
%trace(big sigma_i\otimes\sigma_j)/4

global_declarations;

k = trace(big)/4;
small(1,1) = trace(big*sigxx)/4 + k;
small(1,2) = trace(big*sigxy)/4;
small(1,3) = trace(big*sigxz)/4;

small(2,1) = trace(big*sigyx)/4;
small(2,2) = trace(big*sigyy)/4 + k;
small(2,3) = trace(big*sigyz)/4;

small(3,1) = trace(big*sigzx)/4;
small(3,2) = trace(big*sigzy)/4;
small(3,3) = trace(big*sigzz)/4 + k;