How do you define symbolic variables k, α, β, γ for eigenvalue calculation in MATLAB?

[quansnow]

I use the command eig(A) to calculate the eigenvalues of the matrix A, in which k,α,β,γ are variables,

A=[-0.5*k -i*α 0;-i*α -0.5*γ -i*β;0 i*β -0.5k];
eig(A)

but the MATLAB shows "Undefined function or variable 'k'."
I don't know how to define the variables k,α,β,γ.
Can anyone tell me how to do it? Thanks!

 

[jhae2.718]

syms is a shortcut to the sym() function to create a symbolic variable.

http://www.mathworks.com/help/toolbox/symbolic/sym.html

 

[quansnow]

It works. Thanks a lot!