[BUG] Fix backward independence routing in Mixture sample

[ANANYA542]

Reference Issues/PRs

fixes #974

What does this implement/fix? Explain your changes.

This PR fixes an issue in Mixture._sample where the indep_rows and indep_cols flags were handled in reverse.

Previously, the implementation set rd_size[...] = 1 when the independence flags were True, which caused np.random.choice to draw a single component and broadcast it across the dimension, making it fully dependent. When the flags were False, the full dimension was retained, resulting in independent sampling instead.

This PR corrects the logic by inverting the condition:

if not indep_rows:
    rd_size[0] = 1
if not indep_cols:
    rd_size[1] = 1

This restores the intended behavior where independence retains full sampling dimensions and dependence enforces broadcasting.

Does your contribution introduce a new dependency? If yes, which one?

No

What should a reviewer concentrate their feedback on?

• Whether the updated logic correctly reflects the intended behavior of indep_rows and indep_cols
• Whether the change is consistent with other sampling implementations in the codebase

Did you add any tests for the change?

Tested locally using larger mixture arrays (e.g., 20x2). The output matches expectations:

• dependent settings produce identical rows
• independent settings produce varied rows

Any other comments?

A verification screenshot demonstrating the behavior has also been attached for reference.

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[fkiraly]

Can you explain why it is correct this way round?

[ANANYA542]

@fkiraly —thanks for reviewing
this comes down to how rd_size controls the shape of the component draw before it gets broadcast.If a dimension is set to 1, np.random.choice draws a single component which then gets broadcast across that axis, making it dependent.
In the current implementation this happens when indep_rows=True, so all rows end up sharing the same component, which is the opposite of what we want.Flipping it to if not indep_rows keeps the full dimension when independence is requested, and only collapses it when dependence is intended. Same applies to columns as well.

[ANANYA542]

Hi @fkiraly — just following up on this. I’ve addressed your question above and clarified the reasoning behind the change.Could you please take another look when you have time and let me know if any further clarification or changes are needed?