def install_pip(self, package, save=True, save_dev=False):
        """Installs a pip package.

        :param save: if `True`, pins the package to the Hydrogen requirements
            YAML file.
        :param save_dev: if `True`, pins the package as a development
            dependency to the Hydrogen requirements YAML file.
        :param return: a **single** :class:`Requirement` object, representing
            the installed version of the given package.
        """
        requirement = Requirement.coerce(package)
        click.echo("pip install " + requirement.package)
        cmd = envoy.run("pip install {}".format(str(requirement)))
        if cmd.status_code == 0:
            installed_packages = get_installed_pypackages()
            package = installed_packages[requirement.package]
            requirement.version = "=={}".format(package.version)
            if save:
                self.requirements["all"].add(requirement)
            if save_dev:
                self.requirements["dev"].add(requirement)
            if save or save_dev:
                self.requirements.save()
            return requirement
        else:
            fatal(cmd.std_err)
def mtpa(pmrel, i1max, title='', projection='', ax=0):
    """create a line or surface plot with torque and mtpa curve"""
    nsamples = 10
    i1 = np.linspace(0, i1max, nsamples)
    iopt = np.array([pmrel.mtpa(x) for x in i1]).T

    iqmax, idmax = pmrel.iqdmax(i1max)
    iqmin, idmin = pmrel.iqdmin(i1max)

    if projection == '3d':
        nsamples = 50
    else:
        if iqmin == 0:
            iqmin = 0.1*iqmax
    id = np.linspace(idmin, idmax, nsamples)
    iq = np.linspace(iqmin, iqmax, nsamples)

    torque_iqd = np.array(
        [[pmrel.torque_iqd(x, y)
          for y in id] for x in iq])
    if projection == '3d':
        ax = idq_torque(id, iq, torque_iqd, ax)
        ax.plot(iopt[1], iopt[0], iopt[2],
                color='red', linewidth=2, label='MTPA: {0:5.0f} Nm'.format(
                    np.max(iopt[2][-1])))
    else:
        if ax == 0:
            ax = plt.gca()

        ax.set_aspect('equal')
        x, y = np.meshgrid(id, iq)
        CS = ax.contour(x, y, torque_iqd, 6, colors='k')
        ax.clabel(CS, fmt='%d', inline=1)

        ax.set_xlabel('Id/A')
        ax.set_ylabel('Iq/A')
        ax.plot(iopt[1], iopt[0],
                color='red', linewidth=2, label='MTPA: {0:5.0f} Nm'.format(
                    np.max(iopt[2][-1])))
        ax.grid()

    if title:
        ax.set_title(title)
    ax.legend()