c
c _____________________________
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c
	subroutine presymm(qq,lindex,qresult)
	real qq(4),qresult(4)
	integer lindex
c
	include 'common.f'
	common/a1/ quatsymm(4,48),numsymm
c       PI=3.14159265
c
c  algorithm for forming resultant quaternion
c  from applying a symmetry operator, QUATSYMM(n,lindex)
c  to the first quaternion/rotation
c
c  If the symm oper == O, then
c  Qresult = (O x QQ) where QQ= Q1 x Q2^-1
c  i.e. Qresult = (O x Q1) x Q2^-1
c  note change of signs to get inverse of first orientation
c
	if(lindex.gt.numsymm) stop 'error in presymm, lindex>numsymm'
	if(lindex.lt.1) stop 'error in presymm, lindex<1'
	qresult(1)=quatsymm(4,lindex)*qq(1)+quatsymm(1,lindex)*qq(4)
     &	+quatsymm(3,lindex)*qq(2)-quatsymm(2,lindex)*qq(3)
	qresult(2)=quatsymm(4,lindex)*qq(2)+quatsymm(2,lindex)*qq(4)
     &	+quatsymm(1,lindex)*qq(3)-quatsymm(3,lindex)*qq(1)
	qresult(3)=quatsymm(4,lindex)*qq(3)+quatsymm(3,lindex)*qq(4)
     &	+quatsymm(2,lindex)*qq(1)-quatsymm(1,lindex)*qq(2)
	qresult(4)=quatsymm(4,lindex)*qq(4)-quatsymm(1,lindex)*qq(1)
     &	-quatsymm(2,lindex)*qq(2)-quatsymm(3,lindex)*qq(3)
c
c	write(*,*) 'qresult ',qresult
c
	return
	end
c
c
c _____________________________
c