def METHOD_NAME(polydata, reduction_factor):
    """
    Reduce number of triangles of the given vtkPolyData, based on
    reduction_factor.
    """
    # Important: vtkQuadricDecimation presented better results than
    # vtkDecimatePro
    decimation = vtkQuadricDecimation()
    decimation.SetInputData(polydata)
    decimation.SetTargetReduction(reduction_factor)
    decimation.GetOutput().ReleaseDataFlagOn()
    decimation.AddObserver("ProgressEvent", lambda obj, evt:
                  UpdateProgress(decimation, "Reducing number of triangles..."))
    return decimation.GetOutput()