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# Lorenz example

An example displaying the trajectories for the Lorenz system of equations along with the z-nullcline.

The vector field of the Lorenz system flow is integrated to display trajectories using mlab’s flow function: `mayavi.mlab.flow()`.

The z-nullcline is plotted by extracting the z component of the vector field data source with the ExtractVectorComponent filter, and applying an IsoSurface module on this scalar component.

Python source code: `lorenz.py`

    # Author: Prabhu Ramachandran <prabhu@aero.iitb.ac.in>
    # Copyright (c) 2008-2009, Enthought, Inc.
    # License: BSD Style.

    import numpy
    from mayavi import mlab

    def lorenz(x, y, z, s=10., r=28., b=8. / 3.):
        """The Lorenz system."""
        u = s * (y - x)
        v = r * x - y - x * z
        w = x * y - b * z
        return u, v, w

    # Sample the space in an interesting region.
    x, y, z = numpy.mgrid[-50:50:100j, -50:50:100j, -10:60:70j]
    u, v, w = lorenz(x, y, z)
    fig = mlab.figure(size=(400, 300), bgcolor=(0, 0, 0))

    # Plot the flow of trajectories with suitable parameters.
    f = mlab.flow(x, y, z, u, v, w, line_width=3, colormap='Paired')
    f.module_manager.scalar_lut_manager.reverse_lut = True
    f.stream_tracer.integration_direction = 'both'
    f.stream_tracer.maximum_propagation = 200
    # Uncomment the following line if you want to hide the seed:
    #f.seed.widget.enabled = False

    # Extract the z-velocity from the vectors and plot the 0 level set
    # hence producing the z-nullcline.
    src = f.mlab_source.m_data
    e = mlab.pipeline.extract_vector_components(src)
    e.component = 'z-component'
    zc = mlab.pipeline.iso_surface(e, opacity=0.5, contours=[0, ],
                color=(0.6, 1, 0.2))
    # When using transparency, hiding 'backface' triangles often gives better
    # results
    zc.actor.property.backface_culling = True

    # A nice view of the plot.
    mlab.view(140, 120, 113, [0.65, 1.5, 27])
    mlab.show()

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