def mcmc_nwalkers_vs_ndim_validity_check(nwalkers, ndim):
    """
    Validate mcmc number of walkers and number of vector dimension.
    Has to be satisfied `nwalkers < ndim * 2`.

    :param nwalkers:
    :param ndim:
    :raise: RuntimeError; when condition `nwalkers < ndim * 2` is not satisfied
    """
    if nwalkers < ndim * 2:
        msg = (
            f'Fit cannot be executed with fewer walkers ({nwalkers}) than twice the number of dimensions ({ndim})'
            )
        raise RuntimeError(msg)
