subroutine interp1(X_line,Y_line,X,Y)
! just 1D linear interpolation.
! It is reasonable, if the method of interpolation in accordance with interpolate
! OR alternatively this function serve as probe for PT arguments
	use mod_numres

	implicit none
	real*8, dimension(:), intent(in) :: X_line,Y_line
	real*8, intent(in) :: X
	real*8, intent(out) :: Y

	real*8 tx2
	integer np, ix

	np=SIZE(X_line);
	ix = locate(X_line,X)  ! there function for index search in arbitraty array
	ix=max(ix,1); ix=min(ix,np-1)

	tx2=(X-X_line(ix))/(X_line(ix+1)-X_line(ix))
	Y=(1-tx2)*Y_line(ix)+tx2*Y_line(ix+1)

	return
	end subroutine interp1