I was going through this article about Gaussian processes, in which the author explains about the "variable index" in the form of a plot while writing about 2D Gaussian.
The explanation and plot are as below:
I understood the y-axis in this plot, but I'm having problems understanding the x-axis (variable index).
Where did the values 1 and 2 come from in that axis and how is the y-value
2 for both of them?