# Math Help - Min f (x) d s.t (d^t)d = 1

1. ## Min f (x) d s.t (d^t)d = 1

$
\textup{min} f{}'(x)\textup{ }d$

$s.t \left \| d \right \|_{2}^{2} = 1$
$\textup{show }d = -\frac{f'(x)}{\left \| f(x) \right \|_{2}}$
$\textup{my attempt}$
$\textup{Let } d = (d_{1}, ... ,d_{n})$ $
\newline \textup{constraint = } \sum d^{2}_{i}$
$
\newline \textup{equation = } \sum f'(x)^{2} d^{2}_{i}$
$
\newline \textup{I tryed using lagrangad: using }$
$
L(d, \lambda) = \sum f'(x)^{2} d^{2}_{i}} - \lambda ( \sum d^{2}_{i} - 1)$
but got the wrong anwser

2. I don't understand what the equation you are trying to minimize is.

3. Originally Posted by NOX Andrew
I don't understand what the equation you are trying to minimize is.
Im trying to minimie

(click on the picture)
i assmue minmising withrespect to d