MATLAB: Literal Variables

Control System ToolboxMATLABpolynomialvariables

Hy, I'm an italian Computer Engineering student from Italy and I just started using MATLAB for the work of my bachelor thesis. I'm trying to write some polynomials with literal variables different from x, like these:
A= x^3-b*x^2+a;
B= x^2+a*x-b
I would like then to apply the operations of sum, difference and product between these polynomials. I tried using:
>> syms a;>>S=[1 -1 2];>> G=[1 a 2];>> P= conv(S, G)
but what I obtain is this error message:
Undefined function 'conv2' for input arguments of type 'sym'.Error in conv (line 39)c = conv2(a(:),b(:),shape);
HELLLLP!!!! PLEASEEE!!!! THX 😉

doc sym>sumdoc sym>proddoc sym>diff