code: public void setCoefficient(double coef)
      {
          if(coef <= 0 || Double.isInfinite(coef) || Double.isNaN(coef))
              throw new ArithmeticException("The coefficient must be a positive constant");
          this.coef = coef;
      }
docs: Weights are updated as 1+coef*errors<sup>expo</sup>. This sets the
  coefficient used to update the errors
  
  @param coef the multiplicative factor on the errors in weight construction