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Are you able to run other NEURON tutorials (the pre-build versions)? If not then this issue could be related to the NEURON installation or version. It is possible that using an older version of the NEURON solver is causing the error you mentioned. Please make sure you have the correct version of NEURON installed in your Sim4Life folder. For instance, as you are using Sim4Life version 8.2.0.16876, you should download NEURON using NEURON_setup_8.2.0.16876.exe.

There are two possible ways to change the shape and volume of an organ. First approach uses the "Stretch" option available under the "Move" tool. When following this approach, first create a copy of the tissue you are interested in (e.g. bladder) and use the stretch tool to scale it to the desired dimensions. Afterwards, insert the modified tissue back into the original model by placing it in the proper location while still keeping the original one. When setting up your simulations make sure that the new modified tissue has higher priority compared to the original one and overwrites it. This prevents the introduction of holes. Second approach is via the "Morphing Tool". There is another post showing how to generate a deformation field and how to apply it to the desired organ first and later to the whole body. Please check the following post: https://forum.zmt.swiss/topic/664/morphing-tool-how-it-can-be-used-to-modify-the-shape-of-the-heart

Thanks for the clarification. The code you wrote is correct, I think, and everything behaves normally when I run it (I am using Sim4Life V8.2.2.18061). I do get the squiggly line when the provided values are different (like numpy.array([50.0, 10.0, -900.0])). I get a straight line automatically when the values are all identical (like numpy.array([50.0, 50.0, 50.0])). Some questions for you, so that I can try to reproduce your issue: which version of Sim4Life are you using? which type of simulation are you trying to setup? (it is possible that there is a bug in the API only for some simulation flavours...)