When you click on the "PDE" tag, you're redirected to a new tag "PARTIAL DIFFERENTIAL EQUATIONS". And you find all the old questions that were tagged as "PDE". Except that when you open the page of top users ( here ), all the reputation gained by members answering question tagged as pde is gone. I thought they just changed the name of the tag but this is not the case.

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    $\begingroup$ Here is the post related to the change of the name: Why is the PDE tag abbreviated but not ODE or SDE? (Of course, that does not explain the list of topusers.) $\endgroup$ Commented May 4, 2020 at 15:18
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    $\begingroup$ I know what happened it shoud be fixed soon. I write up an answer. $\endgroup$
    – quid Mod
    Commented May 4, 2020 at 15:19
  • $\begingroup$ Thank you Martin. I just don't undertsand why members have lost privilages and reputation just by changing the name of a tag. All users of PDE tag have to start from zero. @MartinSleziak $\endgroup$ Commented May 4, 2020 at 15:21
  • $\begingroup$ Thank you @quid $\endgroup$ Commented May 4, 2020 at 15:21

1 Answer 1


Technically it was not a change of the name. What happened is that I recently switched the direction of the synonym between and .

It used to be the case that a questions to be tagged was automatically retagged as . Now it is the other way round.

As Martin mentioned that's discussed at Why is the PDE tag abbreviated but not ODE or SDE?

When creating a synonym there are two options, combine it with a merge, that is change the tag on all existing questions, or keep the already tagged questions as they are.

The advantage of the latter is that it is more reversible. That is, when one cancels the synonym the status before the synonym is restored.

Apparently when one switches the direction this is treated as a synonym without merge, which I did not realize and find a bit non-intuitive. So all the questions stayed with and were, it seems, not counted.

I now did the merge and the page should update soon.

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    $\begingroup$ Thank you for your answer Quid. Now it's more clear to me what happened with the pde tag. $\endgroup$ Commented May 4, 2020 at 15:27

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