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| For a real quantity, its absolute value should be equal to the square-root of the quantity squared. Thus, in the example below (i.e., for |u'(x)|), why do I get different functional derivatives? What do I miss something? What is the correct answer?... |
| Thanks but I do not get how your reply answered my question. First, z is not necessarily real; Second, Series produces a multi-valued expansion when it should not. |