悬链线长度
..........\catenary.m
..........\fun_3.m
..........\fun_4.m
..........\fun_5.m
..........\fun_6.m
..........\gauss_int.m
..........\main_2.m
..........\middlepoint.m
..........\sraint.m
..........\traint.m
..........\triang_int.m