# linearShiftFactorFunction Function

## public pure function linearShiftFactorFunction(pos, run, pop) result(f)

### Arguments

Type IntentOptional Attributes Name
integer, intent(in) :: pos
integer, intent(in) :: run
real(kind=dp), intent(in) :: pop

## Source Code

    pure function linearShiftFactorFunction(pos, run, pop) result(f)
! Piecewise-linear scale function for the shift
! Input: pos - position of given determinant in CurrentDets
! Input: run - run for which the factor is needed
! Input: pop - population of given determinant
! Output: f - scaling factor for the shift
integer, intent(in) :: pos
integer, intent(in) :: run
real(dp), intent(in) :: pop
real(dp) :: f, slope

unused_var(pos); unused_var(run)

if (test_flag(CurrentDets(:, pos), get_initiator_flag_by_run(run))) then
f = 1.0
else if (pop < LAS_Sigma) then
f = 0.0
else
if (InitiatorWalkNo .isclose. LAS_Sigma) then
!In this case the slope is ill-defined.
!Since initiators are strictly large than InitiatorWalkNo, set shift to zero
f = 0.0
else
!Apply linear modifcation that equals F1 at Sigma and F2 at InitatorWalkNo
slope = (LAS_F2 - LAS_F1) / (InitiatorWalkNo - LAS_Sigma)
f = (LAS_F1 + (pop - LAS_Sigma) * slope)
end if
end if
end function linearShiftFactorFunction