def _norm_default(x):
    """Default Euclidean norm implementation."""
    # Lazy import to improve `import odl` time
    import scipy.linalg

    if _blas_is_applicable(x.data):
        nrm2 = scipy.linalg.blas.get_blas_funcs('nrm2', dtype=x.dtype)
        norm = partial(nrm2, n=native(x.size))
    else:
        norm = np.linalg.norm
    return norm(x.data.ravel())
Default Euclidean norm implementation.