To cite spca in publications use:

Merola G (2015). “Least Squares Sparse Principal Component Analysis: a Backward Elimination approach to attain large loadings.” Australia & New Zealand Journal of Statistics, 57, 391–429. doi:10.1111/anzs.12128.

Merola G, Chen G (2019). “Projection sparse principal component analysis: An efficient least squares method.” Journal of Multivariate Analysis, 173, 366–382. doi:10.1016/j.jmva.2019.04.001.

Corresponding BibTeX entries:

  @Article{,
    title = {Least Squares Sparse Principal Component Analysis: a
      Backward Elimination approach to attain large loadings},
    author = {Giovanni Maria Merola},
    journal = {Australia & New Zealand Journal of Statistics},
    year = {2015},
    volume = {57},
    pages = {391--429},
    doi = {10.1111/anzs.12128},
  }

  @Article{,
    title = {Projection sparse principal component analysis: An
      efficient least squares method},
    author = {Giovanni Maria Merola and Gemai Chen},
    journal = {Journal of Multivariate Analysis},
    year = {2019},
    volume = {173},
    pages = {366--382},
    doi = {10.1016/j.jmva.2019.04.001},
  }