I am looking to solve the following unconstrained optimization problem:
$$\arg \min_U \|b-A(UY^*)\|_F^2+\lambda\|U\|_1$$
where $\|.\|_F$ is frobenius norm.
I know that the solution without the $\lambda\|U\|_1$ term, will be the least square problem in the form of $AUY^* = b$. How can I solve this problem considering the sparsity constraint.