From 1af1c6a6dbcf1b68f3b4412ab2dce7fc92c749f2 Mon Sep 17 00:00:00 2001
From: Tristan Goodwill <48371600+tristangdwl@users.noreply.github.com>
Date: Mon, 27 Oct 2025 16:24:03 -0400
Subject: [PATCH] get ids associated with an edge in a chunkgraph

---
 chunkie/@chunkgraph/edgeids.m  | 11 +++++++++++
 devtools/test/slicegraphTest.m | 16 +++++++++++++++-
 2 files changed, 26 insertions(+), 1 deletion(-)
 create mode 100644 chunkie/@chunkgraph/edgeids.m

diff --git a/chunkie/@chunkgraph/edgeids.m b/chunkie/@chunkgraph/edgeids.m
new file mode 100644
index 0000000..548888a
--- /dev/null
+++ b/chunkie/@chunkgraph/edgeids.m
@@ -0,0 +1,11 @@
+function ids = edgeids(cgrph, ichs)
+%edgeids return the indices corresponding to points in cgrph.echnks(ichs)
+npts = [cgrph.echnks.npt];
+% get starting index for each edge
+idstart = [1,cumsum(npts)+1];
+
+ids = [];
+for i = 1:length(ichs)
+    ids = [ids, idstart(ichs(i)):(idstart(ichs(i)+1)-1)];
+end
+end
\ No newline at end of file
diff --git a/devtools/test/slicegraphTest.m b/devtools/test/slicegraphTest.m
index 3196d06..79671af 100644
--- a/devtools/test/slicegraphTest.m
+++ b/devtools/test/slicegraphTest.m
@@ -50,4 +50,18 @@ function slicegraphTest0()
 matdiff = norm(sysmat_slc - sysmat(idslce, idslce));
 fprintf('error in sliced system matrix is %e\n',matdiff)
 assert(matdiff < 1e-10)
-end
\ No newline at end of file
+
+
+% test getting ids of edges
+ids = edgeids(cgrph,[3,4,2,1]);
+
+% test values are correct
+assert(all(sort(ids) == (1:sum([cgrph.echnks(1:4).npt]))));
+% test sorted by input list
+assert(~all(sort(ids) == ids));
+
+ids = edgeids(cgrph,ichs);
+% compare edgeids to manual version
+assert(all(ids == idslce));
+
+end