Re: [ccp4bb]: peak search : N dimensions -> 1-dimension

["David J. Schuller" <djs63@cornell.edu>]

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I'm not sure I understood your point.  Are you suggesting we work with 
one-dimensional crystals in order to save CPU time?  I thought that now 
we're living in The Future and computing power is near infinite, we could 
ignore such details.

seriously,
since you are dealing with neighbors in 3-space, you need somehow to refer 
to three coordinate indices.  you can use a one-dimensional array and do 
these calculations explicitly, or you can use a 3-dimensional array and 
let the compiler do the work for you.  personally, i'll put my trust in 
the compiler.  i'm also not sure i would agree with your use of the number 
"MUCH MORE". this number seems too large. i suspect the actual number is 
considerably less than a factor of 2.

you mention a search for the global max.  this is different in that 
neighbors do not need to be considered.


most of the discussion so far seems to be much ado about some small 
details.  why doesn't someone get original and supply an algorithm for
doing this in reciprocal space?


=======================================================================
"Now that I'm a cranky, constipated old man I can afford to say that
 the younger generation of scientists makes me sick to my stomach."
                                                  - C.M. Kornbluth
=======================================================================
                        David J. Schuller
                        modern man in a post-modern world
                        MacCHESS, Cornell University
                        djs63@cornell.edu


On Fri, 11 Jan 2002, Alexandre Urzhumtsev/Ourjoumtsev wrote:

> There is a trick that nobody pointed out during last discussion on the peak 
> search, and I would like to tell about it to young programmers.
> 
> 	At my understanding, there is the only one algorithm - to check the 
> neighbours - but there are numerous its practical realisations which were 
> discussed.
> 
> 	If you do such a search once (or a small number of times), all these 
> computations cost nothing or very little and all codes (except very stupid 
> which we do not discuss) are practically the same. However, if you do this 
> search (or simply a search for the global maximum, etc etc) many-many 
> times, you should not forget that the processing of MULTIdimensional array 
> cost MUCH MORE in CPU than the processing of the ONEdimensional array (of 
> the same total length) in which your data are orginised in your computer in 
> any case.
> 
> 	This switch from multi- to one- dimension became less crucial with the 
> modern computers but there still be problems when this gain in CPU time can 
> be useful.
> 	
> Best regards,
> 
> Sasha