From 550a1c69653aadb4e68202aa6134d6b0b3c6a602 Mon Sep 17 00:00:00 2001
From: Diego Alejandro Tejada Arango
 <12887482+datejada@users.noreply.github.com>
Date: Thu, 19 Sep 2024 13:52:32 +0200
Subject: [PATCH] Refactor group constraints to improve performance (#807)

---
 docs/src/formulation.md  |  2 ++
 docs/src/how-to-use.md   |  6 ++++--
 src/constraints/group.jl | 24 ++++++++++++++++++------
 src/create-model.jl      | 18 ++++++++++--------
 4 files changed, 34 insertions(+), 16 deletions(-)

diff --git a/docs/src/formulation.md b/docs/src/formulation.md
index 94631326..ff1a0dad 100644
--- a/docs/src/formulation.md
+++ b/docs/src/formulation.md
@@ -541,6 +541,8 @@ The following constraints aggregate variables of different assets depending on t
 
 These constraints apply to assets in a group using the investment method $\mathcal{G}^{\text{ai}}$. They help impose an investment potential of a spatial area commonly shared by several assets that can be invested there.
 
+> **Note**: These constraints are applied to the investments each year. The model does not yet have investment limits to a group's accumulated invested capacity.
+
 ##### Minimum Investment Limit of a Group
 
 ```math
diff --git a/docs/src/how-to-use.md b/docs/src/how-to-use.md
index 9a36032f..29061fde 100644
--- a/docs/src/how-to-use.md
+++ b/docs/src/how-to-use.md
@@ -427,8 +427,10 @@ The mathematical formulation of the maximum and minimum investment limit for gro
 -   `invest_method = true`. This parameter enables the model to use the investment group constraints.
 -   `min_investment_limit` $\neq$ `missing` or `max_investment_limit` $\neq$ `missing`. This value represents the limits that will be imposed on the investment that belongs to the group.
 
-    > **Note:**
-    > A missing value in the parameters `min_investment_limit` and `max_investment_limit` means that there is no investment limit.
+    > **Notes:**
+    >
+    > 1. A missing value in the parameters `min_investment_limit` and `max_investment_limit` means that there is no investment limit.
+    > 2. These constraints are applied to the investments each year. The model does not yet have investment limits to a group's accumulated invested capacity.
 
 #### Example
 
diff --git a/src/constraints/group.jl b/src/constraints/group.jl
index c49595d1..8a25afa1 100644
--- a/src/constraints/group.jl
+++ b/src/constraints/group.jl
@@ -1,38 +1,50 @@
 export add_group_constraints!
 
 """
-    add_group_constraints!(graph, Ai, assets_investment, groups)
+    add_group_constraints!(model, graph, ...)
 
 Adds group constraints for assets that share a common limits or bounds
 """
 function add_group_constraints!(model, graph, Y, Ai, assets_investment, groups)
 
-    # - Investment group constraints
+    # - Group constraints for investments at each year
+    assets_at_year_in_group = Dict(
+        group => (
+            (a, y) for y in Y for
+            a in Ai[y] if !ismissing(graph[a].group) && graph[a].group == group.name
+        ) for group in groups
+    )
     @expression(
         model,
         investment_group[group in groups],
         if group.invest_method
             sum(
                 graph[a].capacity * assets_investment[y, a] for y in Y for
-                a in Ai[y] if !ismissing(graph[a].group) && graph[a].group == group.name
+                (a, y) in assets_at_year_in_group[group]
             )
         end
     )
+
+    groups_with_max_investment_limit =
+        (group for group in groups if !ismissing(group.max_investment_limit))
     model[:investment_group_max_limit] = [
         @constraint(
             model,
             investment_group[group] ≤ group.max_investment_limit,
             base_name = "investment_group_max_limit[$(group.name)]"
-        ) for group in groups if !ismissing(group.max_investment_limit)
+        ) for group in groups_with_max_investment_limit
     ]
+
+    groups_with_min_investment_limit =
+        (group for group in groups if !ismissing(group.min_investment_limit))
     model[:investment_group_min_limit] = [
         @constraint(
             model,
             investment_group[group] ≥ group.min_investment_limit,
             base_name = "investment_group_min_limit[$(group.name)]"
-        ) for group in groups if !ismissing(group.min_investment_limit)
+        ) for group in groups_with_min_investment_limit
     ]
 
-    # - TODO: More group constraints
+    # - TODO: More group constraints e.g., limits on the accumulated investments of a group
 
 end
diff --git a/src/create-model.jl b/src/create-model.jl
index b74fcdcc..e27e34b0 100644
--- a/src/create-model.jl
+++ b/src/create-model.jl
@@ -1215,14 +1215,16 @@ function create_model(
         flows_investment,
     )
 
-    @timeit to "add_group_constraints!" add_group_constraints!(
-        model,
-        graph,
-        Y,
-        Ai,
-        assets_investment,
-        groups,
-    )
+    if !isempty(groups)
+        @timeit to "add_group_constraints!" add_group_constraints!(
+            model,
+            graph,
+            Y,
+            Ai,
+            assets_investment,
+            groups,
+        )
+    end
 
     if !isempty(dataframes[:units_on_and_outflows])
         @timeit to "add_ramping_constraints!" add_ramping_constraints!(