symvar(s)
symvar(s,n)
symvar(s) returns a vector of all symbolic variables in s. The variables are
in alphabetical order with uppercase letters preceding lowercase letters.
symvar(s,n) chooses the n symbolic variables in s that are alphabetically
closest to x and returns them in alphabetical order. If s is a symbolic
function, symvar(s,n) returns the input arguments of s before other variables
in s.