aux.rndmissing          Randomly assign NAs to the data matrix with
                        probability 'x'
fill.HardImpute         HardImpute : Generalized Spectral
                        Regularization
fill.KNNimpute          Imputation using Weighted K-nearest Neighbors
fill.OptSpace           OptSpace
fill.SVDimpute          Iterative Regression against Right Singular
                        Vectors
fill.SVT                Singular Value Thresholding for Nuclear Norm
                        Optimization
fill.SoftImpute         SoftImpute : Spectral Regularization
fill.USVT               Matrix Completion by Universal Singular Value
                        Thresholding
fill.nuclear            Low-Rank Completion with Nuclear Norm
                        Optimization
fill.simple             Imputation by Simple Rules
lena128                 lena image at size of (128 x 128)
lena256                 lena image at size of (256 x 256)
lena64                  lena image at size of (64 x 64)
