From 8cb896c9e1106f1d1c3835df843e81375aecf0e5 Mon Sep 17 00:00:00 2001
From: Mason Protter <mason.protter@icloud.com>
Date: Wed, 30 Oct 2024 16:40:54 +0100
Subject: [PATCH] add a `connection_index` function for getting the index of a
 specific connection matrix

---
 src/GraphDynamics.jl | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/src/GraphDynamics.jl b/src/GraphDynamics.jl
index 07bd3c3..aa03eab 100644
--- a/src/GraphDynamics.jl
+++ b/src/GraphDynamics.jl
@@ -32,6 +32,7 @@ end
     isstochastic,
 
     event_times,
+    connection_index
 )
 
 export
@@ -241,6 +242,23 @@ Base.getindex(m::ConnectionMatrices, i) = m.matrices[i]
 Base.length(m::ConnectionMatrices) = length(m.matrices)
 Base.size(m::ConnectionMatrix{N}) where {N} = (N, N)
 
+"""
+    connection_index(ConnType, M::ConnectionMatrices)
+
+give the first index `n` such that `M[n]` is a `ConnectionMatrix{N, ConnType} where {N}`, or throw an error if no such index exists.
+"""
+connection_index(::Type{ConnType}, M::ConnectionMatrices) where {ConnType} = _conn_index(ConnType, M.matrices, 1)
+function _conn_index(::Type{ConnType}, tup::Tuple, i) where {ConnType}
+    if first(tup) isa ConnectionMatrix{N, ConnType} where {N}
+        return i
+    else
+        _conn_index(ConnType, Base.tail(tup), i+1)
+    end
+end
+@noinline _conn_index(::Type{ConnType}, ::Tuple{}, _) where {ConnType} =
+    error("ConnectionMatrices did not contain a ConnectionMatrix with connection type ", ConnType)
+
+
 abstract type GraphSystem end
 
 @kwdef struct ODEGraphSystem{CM <: ConnectionMatrices, S, P, EVT, CDEP, CCEP, Ns, SNM, PNM} <: GraphSystem