c
c  ______________________
c
	subroutine qrvec(qq,din,dout)
c
c  uses quaternion to rotate a vector from DIN to DOUT; 
c  note similarity to above routine
c  note that -q gives the same result as it should (represents same rotation)
c
	real qq(4),din(3),dout(3)
	real t1
c
	t1=qq(4)**2-qq(1)**2-qq(2)**2-qq(3)**2
	do 100, i=1,3
	dout(i)=t1*din(i)
c
		do 90, j=1,3
			dout(i)=dout(i)+(2.*qq(i)*qq(j)*din(j))
c
			if(i.ne.j) then
				do 80, ijk=1,3
					if(i.ne.ijk.and.j.ne.ijk) k=ijk
80				continue
				kl=j-i
				if(kl.eq.2) kl=-1
				if(kl.eq.-2) kl=1
c  poor man"s permutation tensor!
				dout(i)=dout(i)-(2.*qq(k)*qq(4)*float(kl)*din(j))
		endif
90		continue
100	continue
	return
	end
c
c
c _____________________________
c