This is just a quick check: Is the derivative of the function $f(\vec{x})=\vec{x}$ equal to $1$ or the identity matrix? (I know that this question is quite stupid, but I want to get my definitions right...) Thank you.
Dx/dx where x is a vector
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vector-analysis
1 Answers
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If "derivative" means "Jacobi matrix", then it is the identity matrix.
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0@Pete: You might want to study [this wikipedia article](http://en.wikipedia.org/wiki/Derivative#Derivatives_in_higher_dimensions). – 2011-11-22