check_balance           Check covariate balance of the control and
                        treated groups
create_dist_matrix      Create matrix of distances between strata
generate_constraints    Generate constraints to encourage covariate
                        balance
generate_qs             Calculate desired number of controls per
                        stratum
nh0506                  Homocysteine and smoking example data
nh0506_3groups          Homocysteine and smoking example data with
                        multiple control groups
optimize_controls       Select control units that optimize covariate
                        balance
stand                   Standardize covariate vector for balance
                        constraint
