How to use the chempy.cpv.negate function in chempy

# Make settings
    if 'ALPHA' in settings:
        planeObj.extend([ALPHA, settings['ALPHA']])

    if 'COLOR' in settings:
        planeObj.extend([COLOR, settings['COLOR'][0], settings['COLOR'][1], settings['COLOR'][2]])
    else:
        planeObj.extend([COLOR, 0.8, 0.8, 0.8]) # greyish

    planeObj.extend([BEGIN, TRIANGLE_STRIP])
    planeObj.append(NORMAL)

    if 'INVERT' in settings:
        if settings['INVERT']==True:
            planeObj.extend(cpv.negate(normal))
        else:
            planeObj.extend(normal)
    else:
        planeObj.extend(normal)


    for corner in [corner1, corner2, corner3, corner4, corner1]:
        planeObj.append(VERTEX)
        planeObj.extend(corner)
    planeObj.append(END)
    return planeObj

# Make settings
    if 'ALPHA' in settings:
        planeObj.extend([ALPHA, settings['ALPHA']])

    if 'COLOR' in settings:
        planeObj.extend([COLOR, settings['COLOR'][0], settings['COLOR'][1], settings['COLOR'][2]])
    else:
        planeObj.extend([COLOR, 0.8, 0.8, 0.8]) # greyish

    planeObj.extend([BEGIN, TRIANGLE_STRIP])
    planeObj.append(NORMAL)

    if 'INVERT' in settings:
        if settings['INVERT']==True:
            planeObj.extend(cpv.negate(normal))
        else:
            planeObj.extend(normal)
    else:
        planeObj.extend(normal)


    for corner in [corner1, corner2, corner3, corner4, corner1]:
        planeObj.append(VERTEX)
        planeObj.extend(corner)
    planeObj.append(END)
    return planeObj

# define vectors from points
    xyz2 = cpv.sub(xyz2, xyz1)
    xyz3 = cpv.sub(xyz3, xyz1)

    #NB! cpv.get_system2 outputs normalized vectors [x,y,z]
    xyz4 = cpv.get_system2(xyz2,xyz3)
    xyz2 = xyz4[0]
    xyz3 = xyz4[1]
    for x in range(0,3):
        for z in range(0,3):
            if x==z:
                continue
            if xyz4[x]==xyz4[z]:
                raise Exception("Illegal vector settings!")
    xyz4 = cpv.negate(xyz4[2]) #overwrites original

    # transform origin to corner
    if mode==0:
        if npoints_x>1:
            xyz1 = cpv.sub(xyz1, cpv.scale(xyz2,length_x/2))
        if npoints_z>1:
            xyz1 = cpv.sub(xyz1, cpv.scale(xyz3,length_z/2))

    #defines array lines
    nlines=max([npoints_x, npoints_z])
    # in case only one line max

    # create an empty array for xyz entries
    # this may contain more values than are actually drawn later,
    # but they are needed to draw lines in each direction
    grid_xyz = []

Requires python module "numpy".

SEE ALSO

    helix_orientation
    '''
    visualize, quiet = int(visualize), int(quiet)
    import numpy
    stored.x = list()
    cmd.iterate_state(STATE, '(%s) and name CA' % (selection),
                      'stored.x.append([x,y,z])')
    x = numpy.array(stored.x)
    U, s, Vh = numpy.linalg.svd(x - x.mean(0))
    vec = cpv.normalize(Vh[0])
    if cpv.dot_product(vec, x[-1] - x[0]) < 0:
        vec = cpv.negate(vec)
    return _common_orientation(selection, vec, visualize, quiet)

Requires python module "numpy".
 
SEE ALSO
 
    helix_orientation
    '''
    visualize, quiet = int(visualize), int(quiet)
    import numpy
    stored.x = list()
    cmd.iterate_state(-1, '(%s) and name CA' % (selection),
            'stored.x.append([x,y,z])')
    x = numpy.array(stored.x)
    U,s,Vh = numpy.linalg.svd(x - x.mean(0))
    vec = cpv.normalize(Vh[0])
    if cpv.dot_product(vec, x[-1] - x[0]) < 0:
        vec = cpv.negate(vec)
    return _common_orientation(selection, vec, visualize, quiet)

coords = list()
    cmd.iterate_state(state, selection,
            'coords.append([x,y,z])', space=locals())

    if len(coords) < 3:
        print('not enough guide atoms in selection')
        raise CmdException

    x = numpy.array(coords)
    U,s,Vh = numpy.linalg.svd(x - x.mean(0))

    # normal vector of plane is 3rd principle component
    vec = cpv.normalize(Vh[2])
    if cpv.dot_product(vec, x[-1] - x[0]) < 0:
        vec = cpv.negate(vec)

    center = x.mean(0).tolist()
    _common_orientation(selection, center, vec, visualize, 4.0, quiet)

    # plane visualize
    if visualize:
        from pymol import cgo

        dir1 = cpv.normalize(Vh[0])
        dir2 = cpv.normalize(Vh[1])
        sx = [max(i/4.0, 2.0) for i in s]

        obj = [ cgo.BEGIN, cgo.TRIANGLES, cgo.COLOR, 0.5, 0.5, 0.5 ]
        for vertex in [
                cpv.scale(dir1, sx[0]),
                cpv.scale(dir2, sx[1]),