public double op(final double x){
  final double sn=Math.sin(this.asr * (-x + 1) * 0.5);
  return Math.exp((sn * hk - hs) / (1.0 - sn * sn));
}

public double op ( final double x ) { final double sn = Math . sin ( this . asr * ( - x + 1 ) * 0.5 ) ; return Math . exp ( ( sn * hk - hs ) / ( 1.0 - sn * sn ) ) ; }
computes equation 3 , see references
