# minimize frobenius norm subject to rank condition

I'm trying to solve the following problem: Let A be (a, b) matrix. Given l < min ( a, b) , solve:

\begin{align} \min_{rank(X)= l} || A - X ||_{Fro}^2 \end{align} I'm novice in optimization and don't know how to take the rank constraint into account. Thanks!
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