anchor.diff:     stringi_1.1.5.tar.gz \
      magrittr_1.5.tar.gz \
      stringr_1.2.0.tar.gz \
  -   knitr_1.16.tar.gz \
  +   knitr_1.17.tar.gz \
      yaml_2.1.14.tar.gz \
      Rcpp_0.12.12.tar.gz \
      htmltools_0.3.6.tar.gz \
  
positive.code: RUN echo  "deb http://cran.rstudio.com/bin/linux/ubuntu xenial/" >>  /etc/apt/sources.list
  RUN DEBIAN_FRONTEND=noninteractive apt-key adv --keyserver keyserver.ubuntu.com --recv-keys  E084DAB9
  
  RUN apt-get update ; \
      apt-get dist-upgrade -y 
  
  # we want OpenBLAS for faster linear algebra as described here: http://brettklamer.com/diversions/statistical/faster-blas-in-r/
  RUN apt-get install  -y \
  
negative.code: 
  # update the R packages we will need for knitr
  RUN DEBIAN_FRONTEND=noninteractive wget \
     https://mirrors.nics.utk.edu/cran/src/contrib/knitr_1.17.tar.gz \
     https://mirrors.nics.utk.edu/cran/src/contrib/yaml_2.1.14.tar.gz \
     https://mirrors.nics.utk.edu/cran/src/contrib/Rcpp_0.12.12.tar.gz \
     https://mirrors.nics.utk.edu/cran/src/contrib/htmltools_0.3.6.tar.gz \
  