chapter06_ex chapter06_ex\ex6_1.m chapter06_ex\ex6_2.m chapter06_ex\ex6_3.m chapter06_ex\ex6_4.m chapter06_ex\fun_ex6_1.m chapter06_ex\fun_ex6_2.m chapter06_ex\fun_ex6_3.m chapter06_ex\fun_ex6_4.m