say $\displaystyle Y=[y_1,y_2,...y_k]$, where $\displaystyle y_j$ are column vectors. $\displaystyle a=[a_1,a_2...a_k]^t$ is a column vector. Now I have the a polynomial $\displaystyle \frac{1}{k}\sum_{j=1}^{k}a_j^2y_j^ty_j$. Is it possible to express this polynomial in a form of Y and a?