Error: matrix cannot be indexed with

Hello everyone,

I’m using an Octave Kernel on my university’s cluster JupyterLab and I’m getting this error: error: matrix cannot be indexed with .
I’m pretty sure that nothing is wrong with my code, because the code works from time to time and I can see the results but as I mentioned above, sometimes I get that error.
Is there something wrong with the uni server or the problem is on my code?
What do you think?

I am pretty sure that it is not the fault of the JupyterLab interface. I am sorry to inform you: This forum is only about the software applications from the Jupyter project, not about programming.