@Kitonum 

Hi, Thanks for your help, sincerely appreciated.

@taro 

Hi thanks for your help.

Sincerely appreciate.

@acer 

Thanks for your help, it is really a good example.

But please allow me to ask a simple question: what is mean by the command ''u->simplify(u,size)'' ?

Thanks in advance.

@vv

Hi, Thanks for your answer, but i had tried this before but it is not my preferred form.

Do you have any suggestions ? Please share with me.

Thanks in advance. 

@Kitonum 

Hi, Thanks for your answer, but i had tried this before but it is not my preferred form.

Any other suggestions?

How should i get the form of (-x)(A*x^3+B*x^2+C*x+D)?

Thanks in advance.