Consider matrices $Y\in\mathbb{R}^{n\times n}$ and $X\in\mathbb{R}^{n\times m}$ where $m\geq n$. $X$ is unknown but $Y=XX'$, which implies that $Y$ is positive definite (I see no reason why this couldn't alternately be expressed as a positive semi-definite problem with $Y=X'X$, a different $Y\in\mathbb{R}^{m\times m}$ would still be known).
What the easiest method to find $X$? I was thinking of minimizing the Frobenius norm, but wasn't sure if there was some relatively straightforward thing that I'm missing.