Pre-tensioning Cable members in Grasshopper (simple question)

Hi everyone,

Thank you in advance for helping me with it!

I am modeling a cable structure, and made a very simple model that looks like a flag as a test version.

The column part is not a cable member, and the other two lines are cables.

I would like to pre-tension the cable members so that they never go under compression.

However, no matter which value of "initial strain" that I provide to those members, they still take compression.

Aren't the pre-tension supposed to counter-balance the compressive force that is induced in those members?

Please let me know if my understanding is wrong, or how I can fix my model.

Thank you very much!!!!!! I have been working on this simple problem for more than a week, so your help will be greatly appreciated!!

Very Best,

Harry