# A How do i perform differentiation over summation?

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1. Dec 26, 2016

### mahmud_dbm

Last edited: Dec 26, 2016
2. Dec 26, 2016

### Stephen Tashi

It isn't clear what you mean by $\frac{d}{dx} y$. Are you differentiating a vector $y$ with respect to to another vector $x$ ? (If so, how do you define that sort of derivative?) Or are you differentiating a vector of functions of the scalar variable $x$ with respect to $x$ ?

You say that $x$ has exactly N samples. If $x$ is vector of constants, I don't what you would mean by differentiating with respect to $x$. If you have some function $f(x)$ and some set of constants $c_1,c_2,...$ you can talk about forming the derivatives $f'(c_1), f'(c_2),....$.

3. Dec 26, 2016

### mahmud_dbm

You are right, here x is a vector and H is a matrix, and i want to differentiate Hx with respect to x

Here's the complete problem

that's how far i have gone, probably it's wrong.

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4. Dec 27, 2016

### mahmud_dbm

please let me know if it's okay!
that's how far i have gone, probably it's wrong.

5. Dec 31, 2016

### vela

Staff Emeritus

You still haven't explained what $x$ is.