Surjectivity of maps induced on matrices by polynomials and entire functions

Abstract: We determine a necessary and sufficient condition for a polynomial over an algebraically closed field $k$ to induce a surjective map on matrix algebras $M_n(k)$ for $n \ge 2$. The criterion is given in terms of critical points and uses simple linear algebra. Following that, we formulate and prove a corresponding result for entire functions as well.