How to add bold greek symbols?

[jarbet]

How to add bold greek symbols to plot text?

R's plotmath system does not support bold greek symbols: see here from R's Brian Ripley, or from the help page:

Note that bold, italic and bolditalic do not apply to symbols, and hence not to the Greek symbols such as mu which are displayed in the symbol font. They also do not apply to numeric constants.

Example:

How can I make $\beta$ bold?

plot(1, main = expression(bold(beta*'-value')))

Unicode?

Some SO answers suggested trying to use a unicode version of the symbol that is bold. However, all the bold beta symbols I've tried don't render on my Mac..

https://www.fileformat.info/info/unicode/char/search.htm?q=beta&preview=entity
https://www.fileformat.info/info/unicode/char/1d771/index.htm
https://www.fileformat.info/info/unicode/char/1d7ab/index.htm

[jarbet]

Although the bold unicode symbols did not work (see above), thanks @lydiayliu for the following solution: wrap a non-bold unicode symbol in bold():

https://www.fileformat.info/info/unicode/char/03b2/index.htm

plot(1, main = expression(bold("\u03b2"*'-value')))

^{Created on 2023-06-08 by the reprex package (v2.0.1)}

[jarbet]

Also, if you need bold subscripts in expression(bold(...)), just make the subscript a string instead of a number (e.g. log['2'] instead of log[2]):

plot(1, main = expression(bold(log['2']*' mRNA abundance' )))