Date: Wed, 21 Aug 91 14:54:47 -0400
From: djh@ccl.net
To: chemistry@ccl.net
Subject: fitting molecular structures
Status: R

Leif.Laaksonen@vtt.fi (Leif Laaksonen) writes:
>Can somebody give me a pointer to how one fits two molecular structures
>on each other. I can well understand how one calculates the translation
>leading to the smallest least square but how do I calculate the rotation?
>It would of course be just great to receive the piece of code for doing
>the rotation. Are there any other approaches for this problem?

A FORTRAN code of mine (fitest.f) for fitting rigid structures is available
via anonymous ftp on www.ccl.net, in the pub/chemistry/software/fitest.
It uses quaternions to effect the rotation and is not iterative (except for
matrix diagonalization).

Fitest should compile and load on a VAX, Sun, Iris, or CRAY.  Most of
the file is garbage: a main program and subroutines to generate a random
reference and test molecule and fit them.  The useful stuff is the routine
qtrfit.  It should be self-explanatory (ha!).  I haven't been able to extend
the method to work with a series of molecules.
--
David J. Heisterberg            djh@ccl.net             We are NOT all
The Ohio Supercomputer Center   djh@ohstpy.bitnet       Keynesians now.
Columbus, Ohio  43212           ohstpy::djh