c rotate returns the components of a given vector after a right handed screwn rotation of the coordinate system around the nth axis by the angle a
	subroutine rotate(n,a,v)
	dimension v(3)
	aa=a*3.14159265/180
	sina=sin(aa)
	cosa=cos(aa)
	u1=v(1)
	u2=v(2)
	u3=v(3)
	nn=n
	go to (1,2,3),NN
1	v(2)=u2*cosa+u3*sina
	v(3)=u3*cosa-u2*sina
	go to 4
2	v(3)=u3*cosa+u1*sina
	v(1)=u1*cosa-u3*sina
	go to 4
3	v(1)=u1*cosa+u2*sina
	v(2)=u2*cosa-u1*sina
4	if(abs(v(1))-1.0)5,6,6
5	if(abs(v(2))-1.0)7,8,8
7	if(abs(v(3))-1.0)9,10,10
6	v(1)=sign(.9999999,v(1))
	v(2)=0.
	v(3)=0.
	return
8	v(1)=0.
	v(2)=sign(.9999999,v(2))
	v(3)=0.
	return
10	v(1)=0.
	v(2)=0.
	v(3)=sign(.9999999,v(3))
9	return
	end
