To cite package flexclust in publications use:

Leisch F (2006). “A Toolbox for K-Centroids Cluster Analysis.” Computational Statistics and Data Analysis, 51(2), 526–544. doi:10.1016/j.csda.2005.10.006.

Visualization methods are explained in:

Leisch F (2010). “Neighborhood Graphs, Stripes and Shadow Plots for Cluster Visualization.” Statistics and Computing, 20, 457–469. doi:10.1007/s11222-009-9137-8.

Group constraints are explained in:

Leisch F, Grün B (2006). “Extending Standard Cluster Algorithms to Allow for Group Constraints.” In Rizzi A, Vichi M (eds.), Compstat 2006—Proceedings in Computational Statistics, 885–892. ISBN 3-7908-1708-2.

Function qtclust() is explained in:

Scharl T, Leisch F (2006). “The Stochastic QT–clust Algorithm: Evaluation of Stability and Variance on Time–course Microarray Data.” In Rizzi A, Vichi M (eds.), Compstat 2006—Proceedings in Computational Statistics, 1015–1022. ISBN 3-7908-1708-2.

Using flexclust for market segmentation is explained in:

Dolnicar S, Grün B, Leisch F (2018). Market Segmentation Analysis—Understanding It, Doing It, and Making It Useful. Springer, Singapore. doi:10.1007/978-981-10-8818-6.

Corresponding BibTeX entries:

  @Article{,
    author = {Friedrich Leisch},
    title = {A Toolbox for K-Centroids Cluster Analysis},
    journal = {Computational Statistics and Data Analysis},
    year = {2006},
    volume = {51},
    number = {2},
    pages = {526--544},
    doi = {10.1016/j.csda.2005.10.006},
  }

  @Article{,
    author = {Friedrich Leisch},
    title = {Neighborhood Graphs, Stripes and Shadow Plots for Cluster
      Visualization},
    journal = {Statistics and Computing},
    year = {2010},
    volume = {20},
    issue = {4},
    pages = {457--469},
    doi = {10.1007/s11222-009-9137-8},
  }

  @InProceedings{,
    author = {Friedrich Leisch and Bettina Grün},
    title = {Extending Standard Cluster Algorithms to Allow for Group
      Constraints},
    booktitle = {Compstat 2006---Proceedings in Computational
      Statistics},
    pages = {885--892},
    editor = {Alfredo Rizzi and Maurizio Vichi},
    publisher = {Physica Verlag, Heidelberg, Germany},
    isbn = {3-7908-1708-2},
    year = {2006},
  }

  @InProceedings{,
    author = {Theresa Scharl and Friedrich Leisch},
    title = {The Stochastic QT--clust Algorithm: Evaluation of
      Stability and Variance on Time--course Microarray Data},
    booktitle = {Compstat 2006---Proceedings in Computational
      Statistics},
    pages = {1015--1022},
    editor = {Alfredo Rizzi and Maurizio Vichi},
    publisher = {Physica Verlag, Heidelberg, Germany},
    isbn = {3-7908-1708-2},
    year = {2006},
  }

  @Book{,
    author = {Sara Dolnicar and Bettina Grün and Friedrich Leisch},
    title = {Market Segmentation Analysis---Understanding It, Doing It,
      and Making It Useful},
    publisher = {Springer},
    year = {2018},
    address = {Singapore},
    doi = {10.1007/978-981-10-8818-6},
  }