1. ## Partial Derivative

hi everyone,

im trying to do the partial derivate of x^tAx ..please could you see the image? it will make more sense

what i dont know is how they got the partial derivative. and why is it 2a(ii). how did it change to a(ii) from a(ij)

i hope it's clear and Thank you very much everyone

2. Originally Posted by matlabnoob
hi everyone,

im trying to do the partial derivate of x^tAx ..please could you see the image? it will make more sense

what i dont know is how they got the partial derivative. and why is it 2a(ii). how did it change to a(ii) from a(ij)
Are you aware the $\displaystyle a_{ii}$ are the diagnal elements of A?

Also $\displaystyle x^tAx$ is a quadratic form.

3. Originally Posted by pickslides
Are you aware the $\displaystyle a_{ii}$ are the diagnal elements of A?

Also $\displaystyle x^tAx$ is a quadratic form.

i am aware of this, but still do not understand how the partial derivative is done. i thought all you do is ignore the other terms, look at x(i) so you get the sum of a(ij)*x(i) ? but this is not the case here?