code: private String formatCoef(double coef) {
  		double tol = 1e-6; // rounding tolerance
  
  		// zero case
  		if( Math.abs(coef) < tol) {
  			return "0";
  		}
  
  		// integer case
  		long num = Math.round(coef);
  		if( Math.abs(num - coef) < tol) {
  			return Long.toString(num);
  		}
  
  		// Other small cases
  		for(int denom = 2; denom < 12; denom++ ) {
  			num = Math.round(coef*denom);
  			if( num - coef*denom < tol ) {
  				return String.format("%d/%d",num, denom);
  			}
  		}
  
  		// Give up and use floating point;
  		return String.format("%.3f", coef);
  	}
docs: helper function to format simple fractions into rationals
  @param coef
  @return