anchor.diff:      export OMP_NUM_THREADS=2
     '';
   
  -  postInstall = ''
  -    mkdir -p $out/lib/pkgconfig
  -    cp arpack.pc $out/lib/pkgconfig/
  -  '';
  -
  -
     meta = {
       homepage = "https://github.com/opencollab/arpack-ng";
       description = ''
  
positive.code: { lib, stdenv, fetchFromGitHub, cmake
  , gfortran, blas, lapack, eigen }:
  
  stdenv.mkDerivation rec {
    pname = "arpack";
    version = "3.7.0";
  
    src = fetchFromGitHub {
      owner = "opencollab";
      repo = "arpack-ng";
      rev = version;
      sha256 = "1x7a1dj3dg43nlpvjlh8jzzbadjyr3mbias6f0256qkmgdyk4izr";
    };
  
    nativeBuildInputs = [ cmake ];
    buildInputs = assert (blas.isILP64 == lapack.isILP64); [
  
negative.code: 
    cmakeFlags = [
      "-DBUILD_SHARED_LIBS=ON"
      "-DINTERFACE64=${if blas.isILP64 then "1" else "0"}"
    ];
  
    preCheck = if stdenv.isDarwin then ''
  