# My confusion about ##u## and ##\mu##

• B
docnet
TL;DR Summary
Are ##u## and ##\mu## used interchangeably in partial differential equations?
Hi all, I am confused about symbols.

I cannot figure out why my partial differential equations professor writes ##u## and ##\mu## in his lectures. A function ##u(x, y)## turns into ##\mu(x, y)##. His homework sets are always typed with ##u##. I also think he says MYOO during the lectures so it is not just a strange way to write ##u##. He is a Frenchman.

Mentor
2022 Award
##u## and ##\mu## are two very different letters, not only because one is Latin and the other one is Greek, but also because ##\mu ## is the Greek ##m##. I cannot find any ##\mu## in your photo above, and I think it is more a case of sloppy handwriting than it is a case of interchanging the two. However, there are some conventions: ##u## is normally a function, ##\mu## is either an index or a measure. This means that ##\int u\,d\mu## makes sense. But as with all conventions, this is no rule and everybody can use it in a different way.

docnet and sysprog