code: void initMotion(Planar<I> input) {
  		if( solver == null ) {
  			solver = LinearSolverFactory_DDRM.qr(input.width*input.height*input.getNumBands(),6);
  		}
  
  		// compute image derivative and setup interpolation functions
  		computeD.process(input,derivX,derivY);
  	}
docs: Initialize motion related data structures