Homework Help: What does this notation mean?

1. Dec 30, 2008

Firepanda

Say if I have a solid vertical line on the right of partial differential equation, with a subscript to that line, i.e:

d |
dx|y

Hard to write out so I hope you can tell what it is. What does the line mean?

2. Dec 30, 2008

Dick

It generally indicates the variable held constant during the partial differentiation.