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I know very little about vector calculus. What is the derivative of $\langle\alpha,\alpha\rangle$ (dot product) and $\alpha^TK\alpha$ and $\langle\alpha,y\rangle$. All these derivatives are by the variable $\alpha$. Where $K$ is a matrix and $y$ is a vector.

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2 Answers 2

up vote 3 down vote accepted

Just try it yourself by taking component-wise derivatives. You should get $$\alpha\cdot\alpha \Rightarrow 2\alpha$$ and $$\alpha^T K \alpha \Rightarrow 2K\alpha\text{ (if K is symmetric)}$$

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Ok, thanks that worked. –  Benjy Kessler Apr 25 '13 at 10:44
    
Sorry I can't up vote your response, I don't have enough reputation. –  Benjy Kessler Apr 25 '13 at 10:49
    
No problem, great that it helped. –  Matt L. Apr 25 '13 at 11:09
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I found this .pdf very helpful for these types of questions:

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You can make a link by typing [link alias that is displayed](link to item) and filling in between the brackets appropriately. –  Daryl Apr 25 '13 at 11:36
    
There is no space/line break/anything between the closing $]$ and the opening $($. –  Daryl Apr 25 '13 at 11:42
    
@Daryl Maybe you can edit my post so that it works? –  Delvesy Apr 25 '13 at 11:52
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