How to stop a future modification in matlab sym function

Question

Raphael Chinchilla 2018-2-10

0
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https://ww2.mathworks.cn/matlabcentral/answers/381847-how-to-stop-a-future-modification-in-matlab-sym-function

评论： Walter Roberson 2018-2-10

Hi all,

I have been using the symbolic toolbox for a while. I needed to create a symbolic function for an expected value. As matlab does not, at least for now, allow defining properties of arbitrary functions such as:

E(a+b)=E(a)+E(b)

or

E(k*eps)=k*E(eps)

(nor it allows defining variables and constants separately)

I've decided to go and transform my symbolic variable into char, use regular expressions, and then bring it back to symbolic. As I was doing so (the whole process works pretty well), as I ran the code:

result_symbolic=sym(result_char)

I received the following message:

"Warning: Support of character vectors that are not valid variable names or define a number will be removed in a future release. To create symbolic expressions, first create symbolic variables and then use operations on them. "

How can I make them know that there are cases in which it is not possible to actually manually create symbolic, like in the cases there I have worked on?