Subject: Re: CCL:HyperChem and Conjugate Gradient Search Methods

From: Mark D Shenderovich <[email-masked]>
Date: Thu, 17 Apr 1997 10:06:08 -0700 (MST)

On Wed, 16 Apr 1997, patrick kane wrote:

> 
>  Hi,
> 
>  Page 213 of the HyperChem, version 4 manual states that with conjugate 
> gradient search methods, a descent direction (to lower energy) is chosen 
> by consdering [among other things - my brackets] the conjugate of the 
> gradient which is initially the negative of the current gradient.
> 
>  Could someone please tell me what is meant by the CONJUGATE of a gradient.
> 
>  THanks in response for your replies.
> 
>  Rgds,
>  Paddy.

Dear Paddy,

CONJUGATE means that the direction of each iterative step is defined as a
linear combination of gradient vectirs in at least two consequtive points 
of the path, i.e.

	r(i) = a*g(i) + b*g(i-1) + ...

This makes conjugated gradient methods very efficient when a starting
point is far from an energy mimimum. But, if you have a choice, use second
order algorithms (Fletcher-Powel, Newton-Raphson, etc.) when you are close
to a minimum and conjugated gradient becomes too slow.

Yours,

Mark Shenderovich