How to make fonts bigger in **plain tex** math mode?

[Steve Litt]

Philip Taylor (Hellenic Institute) said on Fri, 28 Apr 2023 10:28:32
+0100

>On 28/04/2023 09:42, Steve Litt wrote:
>> Thanks Philip,
>>
>> When I ran your code under luatex, here's what happened:  
>
>Sorry, Steve, you originally wrote "How do I make fonts bigger in 
>**plain tex** math mode", not "[...] in **plain LuaTeX** [...]". Had I 
>known that you were using LuaTeX I would not even have tried to answer 
>your question as I never use LuaTeX simply /because/ it is not 
>compatible with TeX /qua/ TeX.
>
>-- 
>/Philip Taylor/
>

Thanks Philip,

All is not lost. I get almost the same error message when I run it in
the tex executable:

====================================================
[slitt at mydesk plaintex]$ tex philip.tex
This is TeX, Version 3.141592653 (TeX Live 2023) (preloaded format=tex)
(./philip.tex
! Font \sevenrm=cmr7^^c2^^a0 scaled 1440 not loadable: Metric (TFM)
file not fo
und.
<to be read again> 
                   \relax 
l.12 \font\sevenrm=cmr7^^c2^^a0 scaled \magstep 2
                                                 
? 
====================================================

So on my machine, it's reproducible on both the luatex compiler and the
tex compiler. This is a good thing.

Next, I created a Minimal Working Example of the symptom:

#########################################
\font\sevenrm=cmr7  scaled \magstep 2
\end
#########################################

Same error message:
====================================================
[slitt at mydesk plaintex]$ tex junk.tex
This is TeX, Version 3.141592653 (TeX Live 2023) (preloaded format=tex)
(./junk.tex
! Font \sevenrm=cmr7^^c2^^a0 scaled 1440 not loadable: Metric (TFM)
file not fo
und.
<to be read again> 
                   \relax 
l.1 \font\sevenrm=cmr7^^c2^^a0 scaled \magstep 2
                                                
? 
====================================================

Cool. Now we've got the problem trapped to a 2 line TeX file. So I did
what I should have done in the first place and really read the error
message. I think the meaningful part is "Metric (TFM) file not found".

So I went looking for my cmr TFM files:

====================================================
[root at mydesk x86_64-linux]# locate -i \.tfm | grep local | grep 2023 |
grep '/cmr' | grep \.tfm$
/usr/local/texlive/2023/texmf-dist/fonts/tfm/public/cm/cmr10.tfm
/usr/local/texlive/2023/texmf-dist/fonts/tfm/public/cm/cmr12.tfm
/usr/local/texlive/2023/texmf-dist/fonts/tfm/public/cm/cmr17.tfm
/usr/local/texlive/2023/texmf-dist/fonts/tfm/public/cm/cmr5.tfm
/usr/local/texlive/2023/texmf-dist/fonts/tfm/public/cm/cmr6.tfm
/usr/local/texlive/2023/texmf-dist/fonts/tfm/public/cm/cmr7.tfm
/usr/local/texlive/2023/texmf-dist/fonts/tfm/public/cm/cmr8.tfm
/usr/local/texlive/2023/texmf-dist/fonts/tfm/public/cm/cmr9.tfm
/usr/local/texlive/2023/texmf-dist/fonts/tfm/public/figbas/cmrj.tfm
[root at mydesk x86_64-linux]#
====================================================

OK, I have them, but they're not being found. I'm a "do the easy stuff
first" type of guy so I ran texhash as root. No change. I checked all
the files in /usr/local/texlive/2023/texmf-dist/fonts/tfm/public/cm/,
and all were readable by all. The command
texlive search --file cmr7.tfm --global
showed the file at texmf-dist/fonts/tfm/public/cm/cmr7.tfm   .

I changed "scaled \magstep 2" to "scaled 1200", same symptom.

I removed "scaled \magstep 2" and the symptom went away, but
unfortunately, so did the sizing of math fonts.

I tried substituting EURM7 and eurm7 for cmr7, and got the same symptom.

So what we have here is the following file that doesn't compile with
the "tex" executable on my computer, but does compile with the "tex"
executable on your computer:

#########################################
\font\sevenrm=cmr7  scaled \magstep 2
\end
#########################################

I use an up to date Void Linux OS, and installed TeXLive from CTAN, and
updated just now with
tlmgr update --all
as user root, to reproduce the symptom.

So far I haven't been able to narrow it down more than that, except to
say it works on your computer and doesn't work on mine.

Thanks,

SteveT

Steve Litt 
Autumn 2022 featured book: Thriving in Tough Times
http://www.troubleshooters.com/bookstore/thrive.htm