# [Gmsh] Building a cylinder with changing radius

**Francois Lemery**
francois.lemery at gmail.com

*Wed Sep 2 18:04:53 CEST 2015*

Hi, and thank you for the lovely code!
I am trying to build a cylinder with a varying radius, for example in
typical (r,z) coordinates; e.g. r(z)=f(z).
I am going about this by making circular slices which I merge together e.g.:
1st slice: (r,z)=(a1, z1)
2nd slice: (r,z)=(a2, z2)
3rd slice: (r,z)=(a3,z3)
I then make points and lines for each slice, then connect each slice with
lines.
My question is, what is the easiest way to make the surface? I originally
tried to make a Line Loop and Ruled Surface
for a quadrant of the ENTIRE extended cylinder then realized that Line Loop
can take a maximum of 4 lines. Then I tried to combine
two lines together with Compound Line, but GMSH told my Line Loop was wrong!
Worst case scenario is I will build the surface out of individual quadrants
bound between slices; but if there is a simpler way to to this it would be
greatly appreciated!
Merci beaucoup,
François
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