Why do I receive the error "??? No appropriate methods for function ..." when using symbolic functions?

When I execute the following command:

taylor('exp(-x)')

I receive the following error message:

 ??? No appropriate methods for function taylor.

Answer 1

[MathWorks Support Team]

In order to use a symbolic function in MATLAB you must first declare symbolic variables with the SYM command. Please try the following syntax:

syms x

taylor(exp(-x))

Alternately, if you have a numeric value in the variable x and you don't want to overwrite it:

x=0.5;

T=taylor(sym('exp(-x)'))

subs(T)