code: private void computePsiSmooth(GrayF32 ux , GrayF32 uy , GrayF32 vx , GrayF32 vy ,
  								  GrayF32 psiSmooth ) {
  		int N = derivFlowUX.width * derivFlowUX.height;
  
  		for( int i = 0; i < N; i++ ) {
  			float vux = ux.data[i];
  			float vuy = uy.data[i];
  			float vvx = vx.data[i];
  			float vvy = vy.data[i];
  
  			float mu = vux*vux + vuy*vuy;
  			float mv = vvx*vvx + vvy*vvy;
  
  			psiSmooth.data[i] = (float)(1.0/(2.0*Math.sqrt(mu + mv + EPSILON*EPSILON)));
  		}
  	}
docs: Equation 5.  Psi_s