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Tariffs

Ad-valorem tariffs let you price import duties into a network optimization run, so the optimizer weighs a cheaper overseas supplier against the tariff it triggers, the same way it already weighs unit cost against transportation cost.

Declaring countries

A tariff is charged when a unit crosses from one customs territory into another, so the first step is telling SupplyChainModeling which country each Location sits in via the country keyword (an ISO 3166-1 alpha-2 code, e.g. "US", "CN", "DE"):

us = Location(47.608013, -122.335167; country="US")
cn = Location(31.230416, 121.473701; country="CN")

A Location with no country set (the default) never triggers a tariff - existing models that don't use this feature solve exactly as before.

Registering a tariff

add_tariff! registers an ad-valorem rate (a fraction of declared value, e.g. 0.2 for 20%) between two countries, optionally scoped to a single product:

using SupplyChainModeling
using SupplyChainOptimization

sc = SupplyChain()

product = Product("p1")
add_product!(sc, product)

us = Location(47.608013, -122.335167; country="US")
cn = Location(31.230416, 121.473701; country="CN")

customer = Customer("c1", us)
add_customer!(sc, customer)
add_demand!(sc, customer, product, [100.0])

storage = Storage("s1", us; fixed_cost=0.0, opening_cost=0.0, closing_cost=0.0, initial_opened=true)
add_storage!(sc, storage)
add_product!(storage, product)

supplier = Supplier("supplier1", cn)
add_supplier!(sc, supplier)
add_product!(supplier, product; unit_cost=10.0)

add_lane!(sc, Lane(storage, customer; unit_cost=1.0))
add_lane!(sc, Lane(supplier, storage; unit_cost=1.0))

# 20% ad-valorem tariff on anything crossing from CN into US.
add_tariff!(sc, Tariff("CN", "US", 0.2))

minimize_cost!(sc)

get_total_tariff_costs(sc)  # 0.2 * 10.0 (declared value) * 100 (units) == 200.0

Passing product to Tariff (Tariff("CN", "US", 0.2; product=product)) scopes the rate to that product only; every other product moving CN->US is untariffed. A Tariff with product=nothing (the default) applies to every product crossing that border, and a more specific per-product Tariff between the same two countries takes precedence over it.

A lane whose origin and destination resolve to the same country - or where either side has no country set - never incurs a tariff, and a supply chain that never calls add_tariff! solves identically to one without this feature at all: get_total_tariff_costs returns 0.0 and the objective is unaffected.

Declared value

The tariff charged per unit is rate * declared_value, where declared_value is the unit's cost basis at the border: a Supplier's unit_cost or a Plant's unit_cost for product leaving that node, whichever the crossing lane departs from.

Re-exports through a Storage

A Storage blends inventory bought or produced in different countries, so a lane leaving a Storage can't always be tariffed from a single declared origin the way a lane leaving a Supplier/Plant can. The model tracks inventory by country of origin internally for any product with a tariff registered, so a re-export - product that entered a Storage from one country and ships back out crossing into a third - is tariffed against the country it actually originated from, not the Storage's own location:

us = Location(47.608013, -122.335167; country="US")
cn = Location(31.230416, 121.473701; country="CN")
de = Location(52.520008, 13.404954; country="DE")

# ... supplier1 (CN) -> storage (US) -> customer (DE) ...

# No CN->US tariff, so the inbound leg is untariffed - but re-exporting from
# the US storage into DE is, because the goods themselves originated in CN.
add_tariff!(sc, Tariff("CN", "DE", 0.3))

This per-origin tracking is only built for products that actually have a tariff registered somewhere in the network - a supply chain with no tariffs pays no overhead for it (see the "Internals" page for the modeling details).

Reading tariff costs back

  • get_total_tariff_costs(sc) - total tariff cost across the whole horizon, after optimizing.
  • get_financials(sc)'s Tariff_Costs column - the same total, broken out per period, alongside Transportation_Costs/Holding_Costs/Buying_Costs/etc.