public double eccentricity(){
  return Math.sqrt(1 - (semiMinorAxis() * semiMinorAxis()) / (semiMajorAxis() * semiMajorAxis()));
}

public double eccentricity ( ) { return Math . sqrt ( 1 - ( semiMinorAxis ( ) * semiMinorAxis ( ) ) / ( semiMajorAxis ( ) * semiMajorAxis ( ) ) ) ; }
gets the eccentricity of the ellipse , between 0 ( inclusive ) and 1 ( exclusive )
