The baud_rate is 57600, and I have some delay functions in the Arduino code. I cannot change both of them due to the application requirement.
I think I find some explanations:
In the beginning, both the MATLAB and Arduino need sometime to build the connection. This phenomenon occurs both in the MATLAB GUI and M files.
And in MATLAB GUI, if the auto send peroid is too short, the MATLAB can still receive many incomplete data. But if I use a buffer to save the data and judge the length before print it in GUI, this problem can somewhat be solved in the display module.
In the MATLAB M FIles, I just examine the received data with a desired length every time without buffer. So, when the incomplete data coming, MATLAB shows a warning of time. If I want to solve the problem in M files, I can also use a buffer. But it will be more complicated than GUI. Therefore, I decide to use GUI to continue my project.
Thanks for your time.