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

• Mar 1st 2011, 04:15 PM
rosh3000
Min f (x) d s.t (d^t)d = 1
$\displaystyle \textup{min} f{}'(x)\textup{ }d$
$\displaystyle s.t \left \| d \right \|_{2}^{2} = 1$
$\displaystyle \textup{show }d = -\frac{f'(x)}{\left \| f(x) \right \|_{2}}$
$\displaystyle \textup{my attempt}$
$\displaystyle \textup{Let } d = (d_{1}, ... ,d_{n}) $$\displaystyle \newline \textup{constraint = } \sum d^{2}_{i}$$\displaystyle \newline \textup{equation = } \sum f'(x)^{2} d^{2}_{i} $$\displaystyle \newline \textup{I tryed using lagrangad: using }$$\displaystyle L(d, \lambda) = \sum f'(x)^{2} d^{2}_{i}} - \lambda ( \sum d^{2}_{i} - 1)$but got the wrong anwser
• Mar 1st 2011, 05:29 PM
NOX Andrew
I don't understand what the equation you are trying to minimize is.
• Mar 2nd 2011, 12:47 AM
rosh3000
Quote:

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

Im trying to minimie
Attachment 21013
http://www.mathhelpforum.com/math-he...isc/pencil.png(click on the picture)
i assmue minmising withrespect to d