disabling font size trickery in amsart.cls

Question

I know that the ams classes do a lot of font size stuff behind the scenes. Here's my problem: I use some custom fonts for my summation sign, and all that is normally necessary (in the plain old LaTeX report or article class) is the following line in the preamble:

\newcommand{\newsum}{\mathop{\vcenter{\hbox{\huge$\Sigma$}}}}

(yes, I know that TeX normally has different ones for text and math display)

When I typeset a document using amsart.cls, I notice that the summation (and product) signs are smaller than they should be, and that the largest size defined is Huge. What do I need to do to get the summation signs in an amsart.cls to be the same as a regular LaTeX document? (pruning amsart.cls of the font size code is an acceptable answer, but I would rather not have to do something so extreme if there were just one or two lines I could modify)

Answer 1

The reason for your problem is that amsart and article have different definitions of the size commands \large, \Large and so on (which I didn't know until now). Let me assume that you use a base fontsize of 10pt. Then in article you essentially have that \huge means

\fontsize{\@xxpt}{25}\selectfont

where \@xxpt is (not 20 but) 20.74. Thus, you get a fontsize of 20.74pt and a baselineskip of 25pt.

In amsart you have

\fontsize{\@xviipt}{20}\selectfont

instead, where \@xviipt is 17.28, so indeed your summation symbol will be a bit smaller. Now you're in luck since \Huge in amsart is

\fontsize{\@xxpt}{24}\selectfont

(same fontsize, as Carl already saw, but slightly smaller baselineskip), so using \Huge instead of \huge will indeed be your solution in this case. In other cases, you should make a manual choice with \fontsize{##}{##}\selectfont, as Carl suggests in his comment.