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MINOR: [Docs] Refine docs for some compute functions (#44305)



### Rationale for this change

Some trivial inaccurate and missing part in compute functions.

### What changes are included in this PR?

Refined the inaccurate and missing part.

### Are these changes tested?

No need.

### Are there any user-facing changes?

None.

Authored-by: Ruoxi Sun <zanmato1984@gmail.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>