Paper  bibtex   

@misc{ m._steffen_simple_1990,
  title = {A simple method formonotonic interpolation in one dimension},
  url = {http://mesa.sourceforge.net/pdfs/steffen_90.pdf},
  urldate = {2013-05-29},
  author = {{M. Steffen}},
  month = {August},
  year = {1990}
}