code: public static void constraintMatrix3x3( DMatrixRMaj L_3x6 ,
  											DMatrixRMaj L_6x3 ) {
  
  		int index = 0;
  		for( int i = 0; i < 3; i++ ) {
  			L_6x3.data[index++] = L_3x6.get(i,0);
  			L_6x3.data[index++] = L_3x6.get(i,1);
  			L_6x3.data[index++] = L_3x6.get(i,3);
  		}
  	}
docs: Extracts the linear constraint matrix for planar case 2 from the full 4x6 constraint matrix.