MATLAB: Matrix from different expresions

Question

I have a problem with this small program:

syms c h y
E_xi = input ('Enter the function for E:  \n')
    A_xi = input ('Enter the function for A:  \n')
    K_ = ((4*A_xi*E_xi)/L^2) * (L/2) * d
    K = int(K_, xi, -1, 1)

When I enter numbers or variables for E and A: c, h, y – program creat right matrix. When I enter expression: for example x^2 + tk – program gives me error:

Enter the function for E in natural coordinates:  
x^2 + tk
Error using input
Unrecognized function or variable 'x'.
Error in Untitled (line 2)
E_xi = input ('Enter the function for E:  \n') 

How to improve code so that program creat matrix from differnet expressions?

Thank you!

Answer 1

 E_xi=str2sym(input('Enter the function for E:  \n','s'))