sometimes when writing mathematical expression with partial derivatives, one needs to write a vertical bar afterwards and write the value at the which the partial derivatives are being computed as subscripts. See for example the bottom post here:
However, the \mid symbol doesn't produce a tall bar that corresponds to the size of the partial derivatives term. Is there a way to have a taller bar?
PS: Some other posts here mention \middle| but this doesn't compile on my computer.
Thanks in advance....