[Gmsh] How to tell gmsh not to insert new nodes (only use points in .geo file as nodes)?

[明现 赵]

Hello Gmshers:
I am a new user of gmsh, and currently I am trying to make a 3D mesh.
All the points (including surface points and points inside of the volume) are calculated already,
and are defined in the .geo file. Then all the surface points are used to define the surface line loops 
and the triangular plane surfaces. After input to gmsh, the output mesh seems only use surface points
as the tetrahedra nodes, all the points inside the volume are not used to form elements, and there are
many extra point inserted automatically.
But what I want to get is a mesh in which all elements are formed using the points defined in the .geo file,
and there should be no extra points inserted.
Could any one help me, please!

Thanks very much!
                                                                              alpher
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