subroutine flat2(s,nz,ref)
parameter (NSMAX=6827)
real s(NSMAX)
real ref(NSMAX)
nsmo=10
ia=nsmo+1
ib=nz-nsmo-1
do i=ia,ib
call pctile(s(i-nsmo),2*nsmo+1,5,ref(i))
enddo
ref(:ia-1)=ref(ia)
ref(ib+1:)=ref(ib)
return
end subroutine flat2