Dear All in attached image how I can put a vertical line with derivative .Any command for this please?
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....
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