code: public double getVolume() {
  		if (volume!=0) {
  			return volume;
  		}
  		volume =  a*b*c*
  		Math.sqrt(1-Math.cos(alphaRad)*Math.cos(alphaRad)-Math.cos(betaRad)*Math.cos(betaRad)-Math.cos(gammaRad)*Math.cos(gammaRad)
  				+2.0*Math.cos(alphaRad)*Math.cos(betaRad)*Math.cos(gammaRad));
  
  		return volume;
  	}
docs: Returns the volume of this unit cell.
  See http://en.wikipedia.org/wiki/Parallelepiped
  @return