draw a random element from 1:size(this%probs) with the probabilities listed in prob
@param[in] constraint pick only elements from constraint
@param[out] tgt on return, this is a random number in the sampling range of this
@param[out] pos the position of tgt in contain
@param[out] prob on return, the probability of picking tgt from constraint
| Type | Intent | Optional | Attributes | Name | ||
|---|---|---|---|---|---|---|
| class(AliasSampler_t), | intent(in) | :: | this | |||
| integer, | intent(in) | :: | contain(:) | |||
| integer(kind=n_int), | intent(in) | :: | contain_ilut(0:) | |||
| real(kind=dp), | intent(in) | :: | renormalization | |||
| integer, | intent(out) | :: | pos | |||
| integer, | intent(out) | :: | val | |||
| real(kind=dp), | intent(out) | :: | prob |
subroutine constrained_sample_fast(this, contain, contain_ilut, renormalization, pos, val, prob)
class(AliasSampler_t), intent(in) :: this
integer, intent(in) :: contain(:)
integer(n_int), intent(in) :: contain_ilut(0 : )
real(dp), intent(in) :: renormalization
integer, intent(out) :: pos, val
real(dp), intent(out) :: prob
routine_name("constrained_sample_fast")
ASSERT(is_set(contain))
ASSERT(1 <= contain(1) .and. contain(size(contain)) <= size(this%probs%ptr))
ASSERT(renormalization .isclose. (sum(this%get_prob(contain))))
ASSERT(size(contain) == sum(popcnt(contain_ilut)))
if (near_zero(renormalization)) then
pos = 0; val = 0; prob = 1.0
return
end if
if (renormalization < redrawing_cutoff) then
block
type(CDF_Sampler_t) :: cdf_sampler
cdf_sampler = CDF_Sampler_t(this%probs%ptr(contain), renormalization)
call cdf_sampler%sample(pos, prob)
val = contain(pos)
return
end block
end if
val = this%table%sample()
do while (.not. IsOcc(contain_ilut, val))
val = this%table%sample()
end do
pos = int(binary_search_int(contain, val))
prob = this%probs%ptr(val) / renormalization
ASSERT(prob .isclose. (this%probs%ptr(val) / sum(this%probs%ptr(contain))))
end subroutine constrained_sample_fast