code: public void setTolerance(double e_out)
      {
          if(e_out <= 0 || Double.isNaN(e_out))
              throw new IllegalArgumentException("convergence tolerance paramter must be positive, not " + e_out);
          this.tol = e_out;
      }
docs: Sets the tolerance parameter for convergence. Smaller values will be more
  exact, but larger values will converge faster. The default value is
  fairly exact at {@value #DEFAULT_EPS}, increasing it by an order of
  magnitude can often be done without hurting accuracy.
  
  @param e_out the tolerance parameter.