backward set
4.Due to knowledge representation method based on set of rules, forward and backward chaining, depth-first search and the comparison between the diagnosis result deduces by the system and detailed diseases information, the system realized the function of diagnosis, consultation and learning on vegetable diseases.
5.Two methods of edge detection and segmentation based on partial differential equation(PDE) are introduced,they are Snake Model and Level Set Methods. We worked out Euler equation corresponding to Snake using variational method and proved non-stability of the three discrete schemes which are forward differential,backward differential and center differential. We detectd the edge of microscopic cell image by constructing algorithms with upwind differential scheme.

