How do search engines calculate citations when both a preprint and a published journal/conference version of a paper exists? Let's say that I wrote my research paper and then I published it as a preprint on the ArXiv, and I got citations for this preprint. Afterwards, my same paper has been peer reviewed by a journal then published, so, how will search engines count the citations? Will they do a sum or union or consider them as two different papers?
This obviously depends on the indexing service used. Typically, the records for different versions of the same paper are merged, and the service will provide the sum of the references.
For example, on google scholar, you can click on &quot;all versions&quot; to see all versions of a paper included in their record. For example here are the 222 versions of the LIGO GW150914 discovery paper, included in Google's record.
(I am not sure how the extremely rare case that a single work references multiple versions of the same paper is handled. But this should indeed be very rare.)