小编Mak*_*rov的帖子

我正在尝试使用ffmpeg录制VTK 3D动画的视频。我发现http://www.itk.org/Wiki/VTK/Examples/Cxx/Video/FFMPEG的示例对我来说有点奇怪，因为它没有创建渲染，因此不清楚如何在其中附加演员这个案例。所以，我的问题是如何连接vtkRenderer到vtkFFMPEGWriter？我写了一个简化的例子

import vtk

# draw a plane
plane_source = vtk.vtkPlaneSource()
plane_source.SetCenter(0, 0, 0)
plane_source.SetNormal(0, 0, 1)
plane_mapper = vtk.vtkPolyDataMapper()
plane_mapper.SetInput(plane_source.GetOutput())
plane_actor = vtk.vtkActor()
plane_actor.SetMapper(plane_mapper)

# create render
render = vtk.vtkRenderer()
renWin = vtk.vtkRenderWindow()
renWin.AddRenderer(render)
renWin.SetSize(800, 600)
renInter = vtk.vtkRenderWindowInteractor()
renInter.SetRenderWindow(renWin)
render.AddActor(plane_actor)
renWin.Render()
renInter.Initialize()

# set callback
def cb(interactor, event):
    global plane_actor
    plane_actor.RotateZ(0.1)
    interactor.GetRenderWindow().Render()

renInter.AddObserver('TimerEvent', cb)
timerId = renInter.CreateRepeatingTimer(100);

# put something here?
writer = vtk.vtkFFMPEGWriter()
# ??? writer.SetInputConnection(...)
writer.SetFileName("test.avi")
writer.Start()

# run …

我需要使用SymPy来评估表达式:

我希望得到类似的东西

问题是代码

import sympy as sy

n,i,j = sy.symbols('n i j', integer=True)
a = sy.Function('a')

print sy.Sum(sy.Sum(a(j), (j,1,i)), (i, 1, n)).doit()

打印只是双倍总和

Sum(a(j), (j, 1, i), (i, 1, n))