I agree with Gerard. Example: it's unlikely to achieve a result of
rigid-body refinement (when you refine six rotation/translation
parameters) by replacing it with refining individual coordinates using
infinitely large weights for restraints.
Pavel.
On 9/22/10 1:46 PM, Gerard DVD Kleywegt wrote:
> Hi Ian,
>
>> First, constraints are just a special case of restraints in the limit
>> of infinite weights, in fact one way of getting constraints is simply
>> to use restraints with very large weights (though not too large that
>> you get rounding problems). These 'pseudo-constraints' will be
>> indistinguishable in effect from the 'real thing'. So why treat
>> restraints and constraints differently as far as the statistics are
>> concerned: the difference is purely one of implementation.
>
> In practice this is not true, of course. If you impose "infinitely
> strong" NCS restraints, any change to a thusly restrained parameter by
> the refinement program will make the target function infinite, so
> effectively your model will never change. This is very different from
> the behaviour under NCS constraints and the resulting models in these
> two cases will in fact be very easily distinguishable.
>
> --Gerard
>
> ******************************************************************
> Gerard J. Kleywegt
> Dept. of Cell & Molecular Biology University of Uppsala
> Biomedical Centre Box 596
> SE-751 24 Uppsala SWEDEN
>
> http://xray.bmc.uu.se/gerard/ mailto:[log in to unmask]
> ******************************************************************
> The opinions in this message are fictional. Any similarity
> to actual opinions, living or dead, is purely coincidental.
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