I don't know, if this kind of article doesn't explain how to achieve it, it usually needs to be treated with caution, and it is normal to fail to achieve that effect. Other specific details, what function to use, consulting reference books and matlab help documents, can not be clearly stated in a few words or here! There seems to be a reason. There are always people downstairs who like to copy the answers I have made up for many years, even the answers that are not answers. It's annoying!