What does the symbol "$|_{\epsilon=0}$" mean with a derivative?

Question

What does the notation "$|_{\epsilon=0}$" at the bottom of the derivative mean?

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score 2 · Accepted Answer · edited Apr 13 '17 at 12:21

2

It (probably) means you evaluate that derivative in $\epsilon = 0$.

For example, if $f(x) = x^2$, then: $$\frac{df}{dx}\Bigr|_{x=3} = 2x\Bigr|_{x=3} = 6$$

edited Apr 13 '17 at 12:21

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answered Apr 27 '16 at 11:15

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1 Answers1