Re: Bug in PDBSET

[Ian J Tickle <i.tickle@mail.cryst.bbk.ac.uk>]

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On Thu, 5 Mar 1998, Clemens Vonrhein wrote:

> There seem to be problems in PDBSET using the ROTATE MATRIX or
> TRANSFORM command. The SYMGEN card works propperly.
> 
> example ( a symmetry operator from P3(2)21 )
> 
> SYMGEN -Y,X-Y,Z+2/3
> does work
> 
> ROTA MATRIX -
>   0 -1 0 -
>   1 -1 0 -
>   0  0 1
> 
> or
> 
> TRANSFORM FRAC -
>   0 -1 0 -
>   1 -1 0 -
>   0  0 1 -
>   0  0 0.6666667
> 
> don't!
> 
> There is some checking done for
> 1) determinant beeing 1
> 2) matrix multiplied by transpose = unit matrix 1 0 0 0 1 0 0 0 1
> 
> Point 2) gives an error flag:
> 
>     0 -1 0                0  1  0              1 1 0
> A = 1 -1 0        A(T) = -1 -1  0     A*A(T) = 1 2 0
>     0  0 1                0  0  1              0 0 1
>                                                ^^^^^
>                                               ????????
> 

A.A(T) = I if and only if A is orthonormal.  The symmetry matrices applied
to fractional coordinates are not orthonormal for oblique cells (i.e. all
except orthorhombic, tetragonal & cubic); those applied to orthogonal 
coordinates are always orthonormal.

-- Ian

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 Ian J. Tickle, MA, DPhil (Oxon)         | Phone:  (+44) 171 631 6854
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