complex2real is not a MATHWORKS' function. That error message is indicating that MATLAB does not know anything about that function. If that is a function someone has written, then make sure it is on your MATLAB path. Use addpath() or pathtool() to add the folder where that function lives.
If you want the polar form of the Fourier coefficients, you can use
abs(A1) % magnitude
angle(A1) %phase