Friedman, J., Hastie, T., & Tibshirani, R. (2008).
Sparse inverse covariance estimation with the graphical lasso.
Biostatistics, 9, 432-441.
doi: 10.1093/biostatistics/kxm045
#glasso package
Jerome Friedman, Trevor Hastie and Rob Tibshirani (2011).
glasso: Graphical lasso-estimation of Gaussian graphical models.
R package version 1.7.
https://CRAN.R-project.org/package=glasso
Foygel, R., & Drton, M. (2010).
Extended Bayesian information criteria for Gaussian graphical models.
In Advances in neural information processing systems (pp. 604-612).
https://papers.nips.cc/paper/4087-extended-bayesian-information-criteria-for-gaussian-graphical-models
#psych package
Revelle, W. (2014) psych: Procedures for Personality and Psychological Research,
Northwestern University, Evanston, Illinois, USA.
R package version 1.4.4.
https://CRAN.R-project.org/package=psych
#Matrix package
Douglas Bates and Martin Maechler (2014).
Matrix: Sparse and Dense Matrix Classes and Methods.
R package version 1.1-3.
https://CRAN.R-project.org/package=Matrix