From fbafc66e40812fda82ad8ee832713ad1edc477eb Mon Sep 17 00:00:00 2001
From: Greg <11791585+elphick@users.noreply.github.com>
Date: Sat, 25 Jan 2025 09:34:52 +0800
Subject: [PATCH] improved check before solve

---
 elphick/geomet/flowsheet/flowsheet.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/elphick/geomet/flowsheet/flowsheet.py b/elphick/geomet/flowsheet/flowsheet.py
index a5341b9..fd618fc 100644
--- a/elphick/geomet/flowsheet/flowsheet.py
+++ b/elphick/geomet/flowsheet/flowsheet.py
@@ -15,6 +15,7 @@
 import yaml
 from matplotlib import pyplot as plt
 from matplotlib.colors import ListedColormap, LinearSegmentedColormap
+from networkx.algorithms.dag import is_directed_acyclic_graph
 from plotly.subplots import make_subplots
 
 from elphick.geomet import Sample
@@ -306,6 +307,8 @@ def copy_without_stream_data(self):
     def solve(self):
         """Solve missing streams"""
 
+        assert is_directed_acyclic_graph(self.graph), "Graph is not a Directed Acyclic Graph (DAG), so cannot be solved."
+
         # Check the number of missing mc's on edges in the network
         missing_count: int = sum([1 for u, v, d in self.graph.edges(data=True) if d['mc'] is None])
         prev_missing_count = missing_count + 1  # Initialize with a value greater than missing_count