A Block Lanczos with Warm Start Technique for Accelerating Nuclear Norm Minimization Algorithms
For practitioners solving NNM problems, this technique offers a practical speedup without changing the underlying algorithm.
The paper proposes a block Lanczos with warm start (BLWS) technique to accelerate nuclear norm minimization algorithms by reducing the cost of singular value decompositions. Experiments on Robust PCA and Matrix Completion show speedups of at least 2-3x.
Recent years have witnessed the popularity of using rank minimization as a regularizer for various signal processing and machine learning problems. As rank minimization problems are often converted to nuclear norm minimization (NNM) problems, they have to be solved iteratively and each iteration requires computing a singular value decomposition (SVD). Therefore, their solution suffers from the high computation cost of multiple SVDs. To relieve this issue, we propose using the block Lanczos method to compute the partial SVDs, where the principal singular subspaces obtained in the previous iteration are used to start the block Lanczos procedure. To avoid the expensive reorthogonalization in the Lanczos procedure, the block Lanczos procedure is performed for only a few steps. Our block Lanczos with warm start (BLWS) technique can be adopted by different algorithms that solve NNM problems. We present numerical results on applying BLWS to Robust PCA and Matrix Completion problems. Experimental results show that our BLWS technique usually accelerates its host algorithm by at least two to three times.