Section: Function Related Functions
syms = symvar(expr)
where expr is a string containing an expression, such as
'x^2 + cos(t+alpha)'.  The result is a cell array of strings
containing the non-function identifiers in the expression.  Because
they are usually not used as identifiers in expressions, the strings
 'pi','inf','nan','eps','i','j' are ignored.
--> symvar('x^2+sqrt(x)')  % sqrt is eliminated as a function
ans = 
 [x] 
--> symvar('pi+3')         % No identifiers here
ans = 
  Empty array 0 1
--> symvar('x + t*alpha')  % x, t and alpha
ans = 
 [alpha] 
 [t] 
 [x]