subroutine Start_Values()
use work
! computes x(-1), x(-2), x(-3), x(-4), ...
! Via BDF of order 1, 2, 3, 4, ...
real(8) y(n), ff(n), xx(n)

xa(0,:) =x0(:)

y =xa(0,:)
! Membrii 2:
ff(1) =y(2)
ff(2) =-100*y(1) -101*y(2)

! xa(-1): always

! ik =1: xa(-1,:) =(h* ff(:) -c(1,0)*xa(0,:))/c(1,1)

! ik =2: xa(-2,:) =(h* ff(:) -c(2,0)*xa(0,:) --c(2,1)*xa(-1,:))/c(2,2)

! ik =3: xa(-3,:) =(h* ff(:) -c(3,0)*xa(0,:) --c(3,1)*xa(-1,:) -c(3,2)*xa(-2,:))/c(2,2)

! etc.

BDF_do: do ik =1, k-1
!write(10,*) ik

xx =c(ik,0)*xa(0,:)

do l =1, ik-1
xx = xx +c(ik,l)*xa(-l,:)
enddo

xa(-ik,:) =( h*ff(:) -xx )/c(ik,ik)

!write(10,*) xa(-ik,:)
ENDDO BDF_do


END subroutine Start_Values
