Format build.jl

docs/src/problem.md

@@ -66,6 +66,8 @@ The mathematical model employed by RELOG is based on three main components:
 | $K^\text{out-var}_{cmi}$      | Factor used to calculate variable amount of material $m$ collected at center $c$. See `eq_z_collected` for more details.                                                                                         | --             |
 | $K^\text{output}_{pmt}$       | Amount of material $m$ produced by plant $p$ at time $t$ for each tonne of input material processed                                                                                                              | tonne          |
 | $K^\text{storage-limit}_{pm}$ | Maximum amount of material $m$ that can be stored at plant $p$ at any time                                                                                                                                       | tonne          |
+| $K^\text{dem-min}_{mt}$      | Minimum demand of material $m$ at time $t$  | tonne          |
+| $K^\text{dem-max}_{mt}$      | Maximum demand of material $m$ at time $t$  | tonne          |
 | $R^\text{collect}_{cmt}$      | Cost of collecting material $m$ at center $c$ at time $t$                                                                                                                                                        | \$/tonne       |
 | $R^\text{disp}_{umt}$         | Cost to dispose of material at plant/center $u$ at time $t$                                                                                                                                                      | \$/tonne       |
 | $R^\text{em}_{gt}$            | Penalty cost per tonne of greenhouse gas $g$ emitted at time $t$                                                                                                                                                 | \$/tonne       |
@@ -249,6 +251,15 @@ The goal is to minimize a linear objective function with the following terms:
 \end{align*}
 ```
 
+- Plant capacity cannot decrease over time (`eq_capacity_nondecreasing[p.name, t]`):
+
+```math
+\begin{align*}
+& z^\text{exp}_{pt} \geq z^\text{exp}_{p,t-1}
+& \forall p \in P, t \in T
+\end{align*}
+```
+
 - Plant is initially open if initial capacity is positive:
 
 ```math
@@ -317,6 +328,21 @@ The goal is to minimize a linear objective function with the following terms:
 \end{align*}
 ```
 
+- Minimum product demands for products at centers:
+```math
+\begin{align*}
+& \sum_{c : m \in M^-_c} \sum_{u : (u,m) \in E^-(c)} y_{ucmt} \geq K^\text{dem-min}_{mt}
+& \forall m \in M, t \in T
+\end{align*}
+```
+- Maximum product demands for products at centers:
+```math
+\begin{align*}
+& \sum_{c : m \in M^-_c} \sum_{u : (u,m) \in E^-(c)} y_{ucmt} \leq K^\text{dem-max}_{mt}
+& \forall m \in M, t \in T
+\end{align*}
+```
+
 - Calculation of amount collected by the center
   (`eq_z_collected[c.name, m.name, t]`). In the equation below,
   $K^\text{out-var-len}$ is the length of the $K^\text{out-var}_{c,m,*}$ vector.

src/instance/parse.jl

@@ -2,7 +2,7 @@ using JSON
 using OrderedCollections
 
 function parsefile(path::String)::Instance
-    return RELOG.parse(JSON.parsefile(path, dicttype = () -> OrderedDict()))
+    return RELOG.parse(JSON.parsefile(path; dicttype = OrderedDict))
 end
 
 function parse(json)::Instance

src/model/build.jl

@@ -4,13 +4,22 @@
 
 using JuMP
 
-R_expand(p::Plant, t::Int) =
-    (p.capacities[2].opening_cost[t] - p.capacities[1].opening_cost[t]) /
-    (p.capacities[2].size - p.capacities[1].size)
+function R_expand(p::Plant, t::Int)
+    denominator = p.capacities[2].size - p.capacities[1].size
+    if denominator == 0
+        return 0.0
+    end
+    return (p.capacities[2].opening_cost[t] - p.capacities[1].opening_cost[t]) / denominator
+end
 
-R_fix_exp(p::Plant, t::Int) =
-    (p.capacities[2].fix_operating_cost[t] - p.capacities[1].fix_operating_cost[t]) /
-    (p.capacities[2].size - p.capacities[1].size)
+function R_fix_exp(p::Plant, t::Int)
+    denominator = p.capacities[2].size - p.capacities[1].size
+    if denominator == 0
+        return 0.0
+    end
+    return (p.capacities[2].fix_operating_cost[t] - p.capacities[1].fix_operating_cost[t]) /
+           denominator
+end
 
 function build_model(instance::Instance; optimizer, variable_names::Bool = false)
     model = JuMP.Model(optimizer)
@@ -347,6 +356,29 @@ function build_model(instance::Instance; optimizer, variable_names::Bool = false
         )
     end
 
+
+    # Demand bounds (only when active: > 0 for min; finite and > 0 for max)
+    eq_min_demand = _init(model, :eq_min_demand)
+    eq_max_demand = _init(model, :eq_max_demand)
+    for m in products, t in T
+        if m.minimum_demand[t] > 0
+            eq_min_demand[m.name, t] = @constraint(
+                model,
+                sum(
+                    y[src.name, c.name, m.name, t] for c in centers if c.input == m for (src, m2) in E_in[c] if m2 == m
+                ) >= m.minimum_demand[t]
+            )
+        end
+        if isfinite(m.maximum_demand[t]) && m.maximum_demand[t] > 0
+            eq_max_demand[m.name, t] = @constraint(
+                model,
+                sum(
+                    y[src.name, c.name, m.name, t] for c in centers if c.input == m for (src, m2) in E_in[c] if m2 == m
+                ) <= m.maximum_demand[t]
+            )
+        end
+    end
+
     # Plants: Disposal limit
     eq_disposal_limit = _init(model, :eq_disposal_limit)
     for p in plants, m in keys(p.output), t in T
@@ -361,6 +393,13 @@ function build_model(instance::Instance; optimizer, variable_names::Bool = false
         eq_keep_open[p.name, t] = @constraint(model, x[p.name, t] >= x[p.name, t-1])
     end
 
+    # Plants: Capacity cannot decrease over time
+    eq_capacity_nondecreasing = _init(model, :eq_capacity_nondecreasing)
+    for p in plants, t in T
+        eq_capacity_nondecreasing[p.name, t] =
+            @constraint(model, z_exp[p.name, t] >= z_exp[p.name, t-1])
+    end
+
     # Plants: Building period
     eq_building_period = _init(model, :eq_building_period)
     for p in plants, t in T

test/src/model/build_test.jl

@@ -128,6 +128,12 @@ function model_build_test()
           "eq_keep_open[L1,4] : -x[L1,3] + x[L1,4] ≥ 0"
     @test repr(model[:eq_keep_open]["L1", 1]) == "eq_keep_open[L1,1] : x[L1,1] ≥ 1"
 
+    # Plants: Capacity cannot decrease over time
+    @test repr(model[:eq_capacity_nondecreasing]["L1", 4]) ==
+          "eq_capacity_nondecreasing[L1,4] : -z_exp[L1,3] + z_exp[L1,4] ≥ 0"
+    @test repr(model[:eq_capacity_nondecreasing]["L1", 1]) ==
+          "eq_capacity_nondecreasing[L1,1] : z_exp[L1,1] ≥ 150"
+
     # Plants: Building period
     @test ("L1", 1) ∉ keys(model[:eq_building_period])
     @test repr(model[:eq_building_period]["L1", 2]) ==