From d2483a3749d4b6c18746d9618c64e1fbff01d05a Mon Sep 17 00:00:00 2001
From: Martijn Visser <mgvisser@gmail.com>
Date: Mon, 6 Nov 2023 14:14:48 +0100
Subject: [PATCH] set FractionalFlow inflow equal to outflow (#736)

Fixes #733
---
 core/src/solve.jl       | 5 ++++-
 core/test/run_models.jl | 9 +++++++++
 docs/core/usage.qmd     | 2 +-
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/core/src/solve.jl b/core/src/solve.jl
index db3c5c957..90d2cc212 100644
--- a/core/src/solve.jl
+++ b/core/src/solve.jl
@@ -989,7 +989,10 @@ function formulate_flow!(
     for (i, id) in enumerate(node_id)
         downstream_id = only(outneighbors(graph_flow, id))
         upstream_id = only(inneighbors(graph_flow, id))
-        flow[id, downstream_id] = flow[upstream_id, id] * fraction[i]
+        # overwrite the inflow such that flow is conserved over the FractionalFlow
+        outflow = flow[upstream_id, id] * fraction[i]
+        flow[upstream_id, id] = outflow
+        flow[id, downstream_id] = outflow
     end
     return nothing
 end
diff --git a/core/test/run_models.jl b/core/test/run_models.jl
index 69bb3d4ef..893034ae1 100644
--- a/core/test/run_models.jl
+++ b/core/test/run_models.jl
@@ -55,6 +55,15 @@ end
     )
     # flows are recorded at the end of each period, and are undefined at the start
     @test unique(table.time) == Ribasim.datetimes(model)[2:end]
+
+    # inflow = outflow over FractionalFlow
+    t = table.time[1]
+    @test length(p.fractional_flow.node_id) == 3
+    for id in p.fractional_flow.node_id
+        inflow = only(table.flow[table.to_node_id .== id .&& table.time .== t])
+        outflow = only(table.flow[table.from_node_id .== id .&& table.time .== t])
+        @test inflow == outflow
+    end
 end
 
 @testset "basic transient model" begin
diff --git a/docs/core/usage.qmd b/docs/core/usage.qmd
index a0a5e18bb..b20f4987d 100644
--- a/docs/core/usage.qmd
+++ b/docs/core/usage.qmd
@@ -506,7 +506,7 @@ node_id       | Int     | -            | sorted
 active        | Bool    | -            | (optional, default true)
 length        | Float64 | $m$          | positive
 manning_n     | Float64 | $s m^{-\frac{1}{3}}$          | positive
-profile_with  | Float64 | $m$          | positive
+profile_width | Float64 | $m$          | positive
 profile_slope | Float64 | -            | -
 control_state | String  | -            | (optional)