anchor.diff: -{ stdenv
  -, fetchurl
  -, blas
  -, gfortran
  -, liblapack
  -, python }:
  +{ stdenv , fetchurl , blas , gfortran , liblapack , python }:
   
   stdenv.mkDerivation rec {
     pname = "petsc";
  -  version = "3.8.4";
  +  version = "3.12.4";
   
     src = fetchurl {
       url = "http://ftp.mcs.anl.gov/pub/petsc/release-snapshots/petsc-${version}.tar.gz";
  -    sha256 = "1iy49gagxncx09d88kxnwkj876p35683mpfk33x37165si6xqy4z";
  +    sha256 = "1hw4f12v2xwrs37gjh83dbixhg0yxandqx7s7k5vlfx91l9l3aan";
     };
   
     nativeBuildInputs = [ blas gfortran.cc.lib liblapack python ];
  
positive.code:     )
    '';
  
    postInstall = ''
      rm $out/bin/petscmpiexec
      rm $out/bin/popup
      rm $out/bin/uncrustify.cfg
      rm -rf $out/bin/win32fe
    '';
  
    meta = {
      description = "Library of linear algebra algorithms for solving partial differential equations";
      homepage = https://www.mcs.anl.gov/petsc/index.html;
      platforms = stdenv.lib.platforms.all;
      license = stdenv.lib.licenses.bsd2;
    };
  }
  
negative.code:     configureFlagsArray=(
        $configureFlagsArray
        "--CC=$CC"
        "--with-cxx=g++"
        "--with-fc=0"
        "--with-mpi=0"
        "--with-blas-lib=[${blas}/lib/libblas.a,${gfortran.cc.lib}/lib/libgfortran.a]"
  