anchor.diff:  
   FROM base-${PLATFORM} as build
   
  -ARG PETSC_VERSION
  -ARG SLEPC_VERSION
  -
   # add virtualenvironment to install python packages
   RUN python3 -m venv /venv
   
  
positive.code: 
  
  from build as petsc
  
  # install PETSc
  USER root
  
negative.code: 
  from petsc as slepc
  
  ARG SLEPC_VERSION
  
  USER root
  WORKDIR /opt
  RUN curl --no-progress-meter https://slepc.upv.es/download/distrib/slepc-$SLEPC_VERSION.tar.gz | tar xzf -
  