I want to find the $A$ to maximum the value of $tr(A^TSA)$,where $A\in[0,1]^{n\times k},k\le n$, and $S\in R^{n\times n}$ is a symmertic matrix.

Given a $n \times n$ symmetric matrix $\rm S$, solve the optimization problem in $n \times k$ (where $n \geq k$) matrix $\rm X$

$$\begin{array}{ll} \text{maximize} & \mbox{tr} \left( \mathrm X^\top \mathrm S \,\mathrm X \right)\\ \text{subject to} & \mathrm X \in [0,1]^{n \times k}\end{array}$$