anchor.diff:  
   # Build and install ParaView
   ARG PARAVIEW_VERSION=f38113aa2a2a7a7549e1aa5033b546586c07bb74
  -RUN git clone --recursive git://github.com/kitware/paraview.git && \
  +RUN git clone -b $PARAVIEW_VERSION --recursive git://github.com/kitware/paraview.git && \
     cd paraview && \
  -  git checkout $PARAVIEW_VERSION && \
     git submodule update && \
     cd .. && \
     mkdir paraview-build && \
  
positive.code: FROM library/ubuntu:16.04
  MAINTAINER Chris Harris <chris.harris@kitware.com>
  
  ENV NINJA_VERSION v1.7.2
  
  RUN apt-get update && apt-get -y install \
    git \
  
negative.code:   pip install numpy
  
  # Build and install ninja.
  ARG NINJA_VERSION=v1.7.2
  RUN git clone -b $NINJA_VERSION https://github.com/martine/ninja.git && \
    cd ninja && \
    ./configure.py --bootstrap && \
    mv ninja /usr/bin/ && \
    cd .. && \
    rm -rf ninja
  
  # Build and install googletest
  ARG GTEST_VERSION=release-1.8.0
  RUN git clone -b $GTEST_VERSION https://github.com/google/googletest.git && \
    mkdir googletest-build && \
    cd googletest-build && \
    cmake -DCMAKE_INSTALL_PREFIX:PATH=/opt/googletest ../googletest && \
  