A matrix Harnack inequality for semilinear heat equations.

We derive a matrix version of Li & Yau-type estimates for positive solutions of semilinear heat equations on Riemannian manifolds with nonnegative sectional curvatures and parallel Ricci tensor, similarly to what R. Hamilton did in [5] for the standard heat equation. We then apply these estimates to obtain some Harnack-type inequalities, which give local bounds on the solutions in terms of the geometric quantities involved. [ABSTRACT FROM AUTHOR]