Minor fixes to beta function parameters and clarifying text for gamma distribution

[mikegilchrist]

Submission Checklist

• Builds locally -- see below
• [x ] New functions marked with `r since("VERSION")`
• [x ] Declare copyright holder and open-source license: see below

Summary

Minor improvements and fixes to documentation.

Note I get tex build errors which seem unrelated to my changes

$ ./build.py 2 32
render functions-reference as pdf
output file: stan_docs/docs/2_32/functions-reference-2_32.pdf
render functions-reference as html
output dir: stan_docs/docs/2_32/functions-reference
render reference-manual as pdf
output file: stan_docs/docs/2_32/reference-manual-2_32.pdf
render reference-manual as html
output dir: stan_docs/docs/2_32/reference-manual
render stan-users-guide as pdf
Command Rscript -e "bookdown::render_book('index.Rmd', output_format='bookdown::pdf_book')" failed
processing file: _main.Rmd
output file: _main.knit.md
! TeX capacity exceeded, sorry [input stack size=10000]. \font@name -> \T1/bch/b/n/17.28
l.16293 ...org/wiki/Amdahl\textquotesingle{}s_law}
{Amdahl's
Error: LaTeX failed to compile _main.tex. See https://yihui.org/tinytex/r/#debugging for debugging tips. See _main.log for more info.
Execution halted
Traceback (most recent call last):
File "stan_docs/./build.py", line 129, in
main()
File "stan_docs/./build.py", line 125, in main
make_docs(docspath, stan_version, doc, formats)
File "stan_docs/./build.py", line 56, in make_docs
shexec(command)
File "stan_docs/./build.py", line 36, in shexec
raise Exception(ret.returncode)
Exception: 1

Copyright and Licensing

Please list the copyright holder for the work you are submitting (this will be you or your assignee, such as a university or company): Michael Gilchrist

By submitting this pull request, the copyright holder is agreeing to license the submitted work under the following licenses:

• Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)
• Documentation: CC BY-ND 4.0 (https://creativecommons.org/licenses/by-nd/4.0/)

[bob-carpenter]

Thanks for submitting and sorry to have missed this earlier. Other than for making the expectation and variance notation consistent with the rest of our doc these changes look good. I'll just go ahead and fix myself if there's not a response.

[bob-carpenter]

Sorry I didn't see this before. This is fine, but we've used \mathbb{E}[y] for expectations and typically Y for random variables. Also \mathrm{var}[y] (though that may be what \var does?).

[avehtari]

@bob-carpenter were you going to do something more for this?

[bob-carpenter]

Does this need a more formal review? It has a conflict now that needs to be resolved. Happy to review after that.