code: public double getDistance(IdentityByState counts) {
          return (counts.ibs[1]*0.5 + counts.ibs[2])/(counts.ibs[0]+counts.ibs[1]+ counts.ibs[2]);
      }
docs: Distance in genotype space.
  As it is categorical, currently it is just computed as a ratio between shared genotypes and total genotypes.
  Could also be euclidian distance with formula (taken from plink):
  sqrt((IBSg.z1*0.5 + IBSg.z2*2)/(IBSg.z0+IBSg.z1+IBSg.z2*2));
  @param counts
  @return