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Fix issue with Sum constraint #110

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Fix issue with Sum constraint #110

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94 changes: 39 additions & 55 deletions lib/solver/constraints/propagators/sum.ex
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,7 @@ defmodule CPSolver.Propagator.Sum do
args
|> Enum.reduce({0, 0, MapSet.new()}, fn var, {idx_acc, sum_acc, unfixed_acc} ->
next_idx = idx_acc + 1

(fixed?(var) && {next_idx, sum_acc + min(var), unfixed_acc}) ||
{next_idx, sum_acc, MapSet.put(unfixed_acc, idx_acc)}
end)
Expand All @@ -41,80 +42,63 @@ defmodule CPSolver.Propagator.Sum do
filter(all_vars, initial_state(all_vars), changes)
end

def filter(all_vars, %{sum_fixed: sum_fixed, unfixed_ids: unfixed_ids} = _state, _changes) do
{unfixed_vars, updated_unfixed_ids, new_sum} = update_unfixed(all_vars, unfixed_ids)
updated_sum = sum_fixed + new_sum
{sum_min, sum_max} = sum_min_max(updated_sum, unfixed_vars)
def filter(all_vars, %{sum_fixed: sum_fixed, unfixed_ids: unfixed_ids} = _state, changes) do
{updated_unfixed_ids, updated_sum_fixed, sum_min, sum_max} =
apply_changes(all_vars, unfixed_ids, sum_fixed, changes)

case filter_impl(unfixed_vars, sum_min, sum_max) do
:fail -> fail()
:ok -> {:state, %{sum_fixed: updated_sum, unfixed_ids: updated_unfixed_ids}}
end
filter_impl(all_vars, updated_unfixed_ids, sum_min, sum_max)
{:state, %{sum_fixed: updated_sum_fixed, unfixed_ids: updated_unfixed_ids}}
end

defp update_unfixed(all_vars, unfixed_ids) do
Enum.reduce(unfixed_ids, {[], unfixed_ids, 0}, fn pos, {unfixed_acc, ids_acc, sum_acc} ->
defp apply_changes(all_vars, unfixed_ids, sum_fixed, changes) do
Enum.reduce(unfixed_ids, {unfixed_ids, sum_fixed, sum_fixed, sum_fixed}, fn pos,
{unfixed_ids_acc,
sum_acc,
sum_min_acc, sum_max_acc} ->
var = Propagator.arg_at(all_vars, pos)

(fixed?(var) && {unfixed_acc, MapSet.delete(ids_acc, pos), sum_acc + min(var)}) ||
{[var | unfixed_acc], ids_acc, sum_acc}
if Map.get(changes, pos) == :fixed do
min_var = min(var)
sum_min_acc = sum_min_acc + min_var
sum_max_acc = sum_max_acc + min_var
{MapSet.delete(unfixed_ids_acc, pos), sum_acc + min(var), sum_min_acc, sum_max_acc}
else
sum_min_acc = sum_min_acc + min(var)
sum_max_acc = sum_max_acc + max(var)
{unfixed_ids_acc, sum_acc, sum_min_acc, sum_max_acc}
end
end)
end

defp filter_impl(variables, sum_min, sum_max) do
if unsatisfiable(sum_min, sum_max) do
fail()
else
{new_sum_min, new_sum_max} = update_partial_sums(variables, sum_min, sum_max)

## Enforce idempotence: we'll run filtering until there's no changes
((new_sum_min != sum_min ||
new_sum_max != sum_max) && filter_impl(variables, new_sum_min, new_sum_max)) ||
:ok
end
defp filter_impl(variables, unfixed_ids, sum_min, sum_max) do
{new_sum_min, new_sum_max} = update_partial_sums(variables, unfixed_ids, sum_min, sum_max)
test_unsatisfiable(new_sum_min, new_sum_max)
## Enforce idempotence: we'll run filtering until there's no changes
((new_sum_min != sum_min ||
new_sum_max != sum_max) && filter_impl(variables, unfixed_ids, new_sum_min, new_sum_max)) ||
:ok
end

defp update_partial_sums(variables, sum_min, sum_max) do
Enum.reduce(variables, {sum_min, sum_max}, fn v, {s_min, s_max} ->
defp update_partial_sums(variables, unfixed_ids, sum_min, sum_max) do
Enum.reduce(unfixed_ids, {sum_min, sum_max}, fn pos, {s_min, s_max} ->
v = Propagator.arg_at(variables, pos)
min_v = min(v)
max_v = max(v)

new_max = maybe_update_max(v, max_v, removeAbove(v, -(s_min - min_v)))
new_min = maybe_update_min(v, min_v, removeBelow(v, -(s_max - max_v)))
removeAbove(v, -(s_min - min_v))
removeBelow(v, -(s_max - max_v))
new_max = max(v)
new_min = min(v)
new_sum_min = s_min + new_min - min_v
new_sum_max = s_max + max_v - new_max

(unsatisfiable(new_sum_min, new_sum_max) && fail()) ||
{new_sum_min, new_sum_max}
end)
end

## Some optimization: if removeAbove/removeBelow don't change the domain,
## save the additional max/min call.
defp maybe_update_max(_var, current_max, :no_change) do
current_max
end

defp maybe_update_max(var, _current_max, _domain_change) do
max(var)
end

defp maybe_update_min(_var, current_min, :no_change) do
current_min
end

defp maybe_update_min(var, _current_min, _domain_change) do
min(var)
end

defp sum_min_max(sum_fixed, unfixed_variables) do
Enum.reduce(unfixed_variables, {sum_fixed, sum_fixed}, fn v, {s_min, s_max} = _acc ->
{s_min + min(v), s_max + max(v)}
test_unsatisfiable(new_sum_min, new_sum_max)
{new_sum_min, new_sum_max}
end)
end

defp unsatisfiable(sum_min, sum_max) do
sum_min > 0 || sum_max < 0
defp test_unsatisfiable(sum_min, sum_max) do
(sum_min > 0 || sum_max < 0) && fail()
end

defp fail() do
Expand Down