About the surname Yos(h)ida I have recently bumped into the Japanese mathematician {}{}. I was wondering two things about his surname: 1. Why is it so often spelt _Yosida_ instead of _Yoshida_? And taking lead from it, when did change sound from /si/ to /ɕi/? That is, is it possible that at the time this mathematician was working his name was actually read /Josida/, hence the spelling? Or is it an older scheme of transliteration that stuck for some reason? 2. Where should I stress Yoshida? /'joɕida/, /jo'ɕida/ or /joɕi'da/? Naturally, the answer to this lies in the Japanese pitch accent, so how is the pitch accent of this particular word?

1. Spelling conventions are different. It's almost certainly not the case that the pronunciation has changed since then, as evidence suggests that /si/ has been [ɕi] since Old Japanese in the 700s (and also suggests that /se/ was once [ɕe], meaning that the overall direction might well be from [ɕ] to [s] rather than the other way around). Some romanisation systems (such as Hepburn) prefer to represent as accurate a pronunciation as can be conveyed in letters (hence ‹shi›); other systems prefer either internal regularity or 1:1 phoneme-to-letter correspondences (giving ‹si› to be consistent with ‹sa› etc). These days the most common system for names is some variant of Hepburn; this was not always the case in the past (which is likely why your mathematician's name isn't in proper Hepburn).

2. As for the accent, my (admittedly non-native) gut instinct suggests [jòɕídá] or [jòɕídà] and [kóòsàkù]. Others can correct me.