At present , the difficulty of the study of tunnel include five factors , first , the unclear model , second , the indistinct criteria , third , all of the problem that we are facing being limited information , the forth , limited knowing of destruction mechanism , the fifth , much indefinites 目前隧道结构失稳研究的困难在于失稳模型不清楚，失稳判据不明确，面对的是“数据有限”的问题，且对岩体本身的破坏机理了解有限，存在大量的不确定性。
The most difficult thing in automatic extraction of roads in sar image is that we have to face various disturbance , including not only those beside roads such as automobiles 、 trees and street lamps , etc . , but also speckle which floods in the whole sar image 从sar图像中自动提取主干道路的困难在于, sar图像中存在着大量的干扰。这些干扰既包括来自道路目标附近的干扰,如汽车、树木和路灯等等,也包括充斥于整幅图像的相干斑噪声,相干斑给sar图像的解译造成了极大的困难。
The difficulties in studying the coordination for multiple robots is that all joints of robot are no longer independent because of the constraints by the touch between the robot and object and that the new system consisting of robot and object no longer owns some good characters by single robot such passity as so on . therefore some control algorithms being suitable for single robot is not probably avail for multiple robots 多个机器人协调控制的困难在于：多个机器人与物体接触形成的约束关系使得机器人的各关节不再独立，也使得由机器人与物体组成的新系统不再拥有单个机器人具有的一些很好的特性，如被动性等，因此适应于单个机器人的控制法可能对多个机器人失效。
A main difficult in topology optimization is the singular optimum exists , which performs dimensions mutated and un - connectively in spatial domain ( the singular optimum point was hard to get ) . so topology optimization is as regarded as a global optimization problem in concave feasible fields 拓扑优化的主要困难在于其可行域的奇异性，该奇异性表现为可行域在某些点维数突变及可行域非连通(而奇异点往往难以被搜索到) ，因此拓扑优化也可看作是在非凸可行域的全局最优问题。
