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Can you explain what does $ \frac{\partial}{\partial x^i}$ means?

Nazar Serdyuk
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    It is a partial derivative (https://en.wikipedia.org/wiki/Partial_derivative) with respect to variable $x^i$. – Gareth Mar 13 '14 at 14:37
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    What a bad (replace bad with curse word) notation for the coordinates. – Git Gud Mar 13 '14 at 14:41
  • this book is very confusing – ILoveMath Mar 13 '14 at 14:42
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    @GitGud The notation $x^k$ for coordinates isn't that bad. For example, $x=\sum x^ke_k$ represents an element of $\mathbb R^n$, while $f=\sum f_ke^k$ represents a linear functional on $\mathbb R^n$. I saw that in other books, say, Spivak's Calculus on Manifolds. – Yai0Phah Mar 13 '14 at 14:54
  • @GitGud Another reference: http://en.wikipedia.org/wiki/Einstein_notation – Yai0Phah Mar 13 '14 at 14:56
  • @FrankScience Not surprisingly your references are mainly related to physics, which supports my claim. – Git Gud Mar 13 '14 at 14:57

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