https://doi.org/10.1351/goldbook.10083
Solution to the multivariate decomposition of a data matrix in which iteratively a solution of one output matrix is used to compute the second matrix, after the application of constraints.
Note: ALS is used to decompose multiple spectra (\(\boldsymbol{X}\)) into concentration (\(\boldsymbol{C}\)) and component spectra (\(\boldsymbol{S}\)). \(\boldsymbol{X} = \boldsymbol{C}\boldsymbol{S}^{\rm{T}}\). Because spectra and concentrations cannot be negative at each iteration negative values are set to zero.