def freeze(h, output_yaml, resolve, groups):
    """Output installed packages."""
    if not groups:
        groups = filter(lambda group: not group.lower().startswith("bower"),
                        h.requirements.keys())
    else:
        groups = [text_type.strip(group) for group in groups.split(",")]

    if output_yaml:
        for requirements in h.requirements.values():
            for requirement in requirements:
                if resolve and not requirement.version:
                    requirement.load_installed_version()
        click.echo(h.requirements.yaml)
    else:
        for group in groups:
            if not h.requirements[group]:
                continue
            click.echo("# {}".format(group))
            for requirement in h.requirements[group]:
                if resolve and not requirement.version:
                    requirement.load_installed_version()
                click.echo(str(requirement))
def airgap_fft(airgap, bmin=1e-2, ax=0):
    """plot airgap harmonics"""
    unit = 'T'
    if ax == 0:
        ax = plt.gca()
    ax.set_title('Airgap Flux Density Harmonics / {}'.format(unit))
    ax.grid(True)
    order, fluxdens = np.array([(n, b) for n, b in zip(airgap['nue'],
                                                       airgap['B_nue']) if b > bmin]).T
    try:
        markerline1, stemlines1, _ = ax.stem(order, fluxdens, '-.', basefmt=" ",
                                             use_line_collection=True)
        ax.set_xticks(order)
    except ValueError:  # empty sequence
        pass