Given a matrix valued function $f_t:\mathbb R^{N\times N} \mapsto \mathbb R^{N\times N}$. For $f_t(A)=B$ both $A$ and $B$ are symmetric. Which properties can be assigned to $f_t$, when the following division $$ \frac{\det(f_t(A))}{(1-t^2)^{N/2}} $$ will again result in a polynomial. Should a polynomial $f_t(\cdot)$ have some restrictions on the coefficients?
To give an explicit example (see here): Is $\displaystyle \frac{\det((1+2t^2)I - At)}{(1-t^2)^{N/2}}$ expressible as polynomial?