def load(self, filename, create_if_missing=True):
        filename = Path(filename)
        if not filename.exists() and create_if_missing:
            self.load_pip_requirements()
            with filename.open("w") as f:
                f.write(yaml.dump(self.serialized, default_flow_style=False,
                                  encoding=None))
            self.filename = filename
            return self.save(filename)
        with filename.open() as f:
            for group, requirements in yaml.load(f.read()).items():
                for requirement in requirements:
                    self[group].add(Requirement.coerce(requirement))
        self.filename = filename
def mmf(f, title='', ax=0):
    """plot magnetomotive force (mmf) of winding"""
    if ax == 0:
        ax = plt.gca()
    if title:
        ax.set_title(title)
    ax.plot(np.array(f['pos'])/np.pi*180, f['mmf'])
    ax.plot(np.array(f['pos_fft'])/np.pi*180, f['mmf_fft'])
    ax.set_xlabel('Position / Deg')

    phi = [f['alfa0']/np.pi*180, f['alfa0']/np.pi*180]
    y = [min(f['mmf_fft']), 1.1*max(f['mmf_fft'])]
    ax.plot(phi, y, '--')
    alfa0 = round(f['alfa0']/np.pi*180, 3)
    ax.text(phi[0]/2, y[0]+0.05, f"{alfa0}°",
            ha="center", va="bottom")
    ax.annotate(f"", xy=(phi[0], y[0]),
                xytext=(0, y[0]), arrowprops=dict(arrowstyle="->"))
    ax.grid()