!  GeP3rot.f90
!
!  Axel Drees, Uni Heidelberg, September 1997
!
!   Rotate vector into new coordinate system
!
function GeP3rot (p3old, costh, sinth, cosph, sinph)
    use genesis_m, self=>GeP3rot
    use f90_kind
    use mom_m
    implicit none
    type(mom3)                     :: GeP3rot
    type (mom3), intent(in)        :: p3old
    real (kind=double), intent(in) :: costh, sinth, cosph, sinph

! make new vector by rotating old one with anti-clockwise Euler angles
    GeP3rot%px =  p3old%px*costh*cosph - p3old%py*sinph + p3old%pz*sinth*cosph
    GeP3rot%py =  p3old%px*costh*sinph + p3old%py*cosph + p3old%pz*sinth*sinph
    GeP3rot%pz = -p3old%px*sinth                        + p3old%pz*costh

end function GeP3rot