How can I extract variable from equation from gui

I want to extract formula equation from user key-in in gui. for example a+a+b. The matlab will extract the variable a and b. and ask user to key in the value. the user can either key in the value or new equation. for example a= 2.

Answer 1

[Walter Roberson]

symvar()

[Hazwan Arif Mazlan]

if i use symvar(), can i assign value or another expression to sym variable?

[Walter Roberson]

http://matlab.wikia.com/wiki/FAQ#How_can_I_create_variables_A1.2C_A2.2C....2CA10_in_a_loop.3F