c
c _____________________________
c
c
	subroutine postsymm(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 second quaternion
c
c  If the symm oper == O, then
c  Qresult = (QQ x O^-1) where QQ= Q1 x Q2^-1
c  i.e. Qresult = Q1 x (O x Q2)^-1
c  note change of signs to get inverse of first orientation
c
	if(lindex.gt.numsymm) stop 'error in postsymm, lindex>numsymm'
	if(lindex.lt.1) stop 'error in postsymm, lindex<1'
	qresult(1)=qq(1)*quatsymm(4,lindex)-qq(4)*quatsymm(1,lindex)
     &	+qq(2)*quatsymm(3,lindex)-qq(3)*quatsymm(2,lindex)
	qresult(2)=qq(2)*quatsymm(4,lindex)-qq(4)*quatsymm(2,lindex)
     &	+qq(3)*quatsymm(1,lindex)-qq(1)*quatsymm(3,lindex)
	qresult(3)=qq(3)*quatsymm(4,lindex)-qq(4)*quatsymm(3,lindex)
     &	+qq(1)*quatsymm(2,lindex)-qq(2)*quatsymm(1,lindex)
	qresult(4)=qq(4)*quatsymm(4,lindex)+qq(1)*quatsymm(1,lindex)
     &	+qq(2)*quatsymm(2,lindex)+qq(3)*quatsymm(3,lindex)
c
c	write(*,*) 'postsymm: qresult ',qresult
c
	return
	end
c
c
c _____________________________
c