code: public void setEta(double eta)
      {
          if(Double.isNaN(eta) || eta < 0.5 || eta > 1.0)
              throw new IllegalArgumentException("eta must be in [0.5, 1] not " + eta);
          this.eta = eta;
          this.phi = Normal.invcdf(eta, 0, 1);
          this.phiSqrd = phi*phi;
          this.zeta = 1 + phiSqrd;
          this.psi  = 1 + phiSqrd/2;
      }
docs: SCW uses a probabilistic version of the margin and attempts to make a
  correction so that the confidence with correct label would be of a
  certain threshold, which is set by eta. So the threshold must be in
  [0.5, 1.0]. Values in the range [0.8, 0.9] often work well on a wide
  range of problems
  
  @param eta the confidence to correct to