MATLAB: Do I receive this error “Support of character vectors that are not valid variable names or define a number will be removed in a future release. “

symbolic

I'm trying to differentiate an expression f which has a horrible coefficient, specifically, (4/3)^(5/6). I want to prevent matlab from giving me the answer to diff(f,x) in the form of an incomprehensible rational number. I can accomplish my objective as follows.
f = @(x) sym('(4/3)^(5/6)')*x^(2/3)
and then
   simplify(diff(f,x))
returns
   (4*2^(2/3)*3^(1/6))/(9*x^(1/3))
which is exactly what I want. However, it's accompanied by a stern warning:
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. 
  > In sym>convertExpression (line 1559)
    In sym>convertChar (line 1464)
    In sym>tomupad (line 1216)
    In sym (line 179)
    In @(x)sym('(4/3)^(5/6)')*x^(2/3)
    In sym>funchandle2ref (line 1308)
    In sym>tomupad (line 1206)
    In sym (line 179)
    In sym/privResolveArgs (line 921)
    In sym/diff (line 21)
I can turn off the warning, but I don't want this functionality to go away, as threatened, in future releases. Is there a way to accomplish the same result without triggering the warning?

Best Answer

(sym(4)/3)^(sym(5)/6)*x^(sym(2)/3)
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