This page lists some of the most common difficulties encountered in installing and running PyClaw. If you do not find a solution for your problem here, please e-mail the claw-users Google group. You may also wish to consult the list of known issues.

Compilation errors

Two frequent sources of compilation error are:

  • Your environment variable FC is set to g77 or another Fortran 77 compiler. FC should be undefined or set to a Fortran 90 compiler. If you have installed gfortran, you could set:

    $ export FC = gfortran

in your .bash_profile (in mac) or .bashrc (in linux).

  • Conflicts between 32-bit and 64-bit files. This has been encountered on Mac OS X with 32-bit Enthought Python. We recommend using a 64-bit Python install, such as that available from Enthought (free for academics). The 32-bit EPD has also been known to cause a plotting issue with PyClaw in which plotting becomes extremely slow.

Use Fortran-ordered arrays

By default, Numpy arrays use C-ordering. But the arrays that store the solution and coefficients in PyClaw (i.e., q and aux) must be initialized using Fortran ordering, for compatibility with the Fortran routines and PETSc. Ordinarily, this is handled automatically when you create a State or Solution object. If you are manually creating arrays, be sure to pass the flag ‘F’ to specify Fortran ordering.


When installing Clawpack, if you get an error message saying that lblas or llapack is not found, please update your installation of Numpy to at least version 1.8. You can do this via:

pip install -U numpy

Then try the installation again.