Do you know any software (online or not) easy to understand and appropriate to create this kind of plots?

I would like the image to be vectorized, can write subindices, arrows, dots and so on to explain numerical stencils and grids.
Do you know any software (online or not) easy to understand and appropriate to create this kind of plots?

I would like the image to be vectorized, can write subindices, arrows, dots and so on to explain numerical stencils and grids.
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