Fix pantelides-with-ag corner case #2009
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Fixes the corner case mentioned in the doc comment. In partiuclar, when we have an incomplete alias chain, the alias can change which variable needs to be considered the highest-differentiated. While we're at it, also take care of the todo in the same place.
We're using augmenting path construction here to try to find a maximal matching of the variables at the given differentiation level. However the construct_augmenting_path! function assumes as a pre-condition that eq-color is reset to zero in order for it to actually produce an augmenting path. Failing to do this can cause it to falsely declare a system singular.
YingboMa
reviewed
Jan 3, 2023
| # Invariant from alias elimination: Stem is chosen to have | ||
| # the highest differentiation order. | ||
| @assert stem′ !== nothing | ||
| if !haskey(ag, var′) || ag[var′][2] != stem′ |
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Could you add an ASCII diagram to show why this is true and why the clean up step is needed in comments?
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ASCII diagram explaining why which condition is true?
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No, I'm asking which condition you want explained.
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Maybe just explain the general process and why the clean up at the end is necessary?
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The cleanup is just addressing the # TODO: remove lower diff vars from whitelist that was already there, but I can expand the comments a bit.
YingboMa
approved these changes
Jan 29, 2023
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Fixes the corner case mentioned in the doc comment. In partiuclar, when we have an incomplete alias chain, the alias can change which variable needs to be considered the highest-differentiated. While we're at it, also take care of the todo in the same place.