subroutine pctile(x,npts,npct,xpct)
real x(npts)
real,allocatable :: tmp(:)
allocate(tmp(npts))
tmp=x
call shell(npts,tmp)
j=nint(npts*0.01*npct)
if(j.lt.1) j=1
if(j.gt.npts) j=npts
xpct=tmp(j)
continue
return
end subroutine pctile