To cite flexsurv in publications use:
Christopher Jackson (2016). flexsurv: A Platform for Parametric Survival Modeling in R. Journal of Statistical Software, 70(8), 1-33.<doi:10.18637/jss.v070.i08>
Corresponding BibTeX entry:
@Article{, title = {{flexsurv}: A Platform for Parametric Survival Modeling in {R}}, author = {Christopher Jackson}, journal = {Journal of Statistical Software}, year = {2016}, volume = {70}, number = {8}, pages = {1--33}, doi = {10.18637/jss.v070.i08}, }