Plot Beta
=========

The following example shows how to use pymad to plot the beta functions for the LHC for injection and collision optics::

    from matplotlib import pyplot
    from cern import pymad

    def plot_beta(model, postfix=''):
        # Run twiss on the model, optionally give name of file
        # where tfs table is stored
        result, summary = model.twiss(seqname='lhcb1',
                                      columns=['name', 's', 'betx', 'bety'],
                                      file='lhcb1' + postfix + '.tfs')

        pyplot.figure()
        # do something with the result (note, madx is still waiting!):
        pyplot.xlabel('dist. from IP1')
        pyplot.ylabel(r'$\beta$')
        pyplot.plot(result.s, result.betx, label=r'$\beta_x$')
        pyplot.plot(result.s, result.bety, label=r'$\beta_y$')
        pyplot.savefig('beta' + postfix + '.eps')


    # choose the mode
    mode = 'jpymad'
    #mode = 'cpymad'

    mdefname = 'lhc'
    opticname = 'injection'

    #
    # Here it starts
    #
    # create the PyMad Service
    pms = pymad.init(mode)

    # print the name of all model definitions
    print pms.mdefnames

    # alternatively use convenience function
    #pymad.ls_mdefs()

    # get one model-definition
    model = pms.create_model(mdefname)

    # alternatively: create the model by name and get the model definition afterwards:
    # model = pms.create_model(mdefname)
    # mdef = model.mdef

    # list the available (running) models
    pymad.ls_models()

    # print a list of available sequences:
    print mdef.seqnames

    plot_beta(model, '_inj')

    # list the available optics and set a new one
    print mdef.opticnames
    model.set_optic(opticname)

    plot_beta(model, '_coll')

    # remove the model from the service:
    pms.delete_model(model)

    # and do a cleanup
    pymad.cleanup()