Added matplotlib as an *optional* dependency since now at least one example generates figures.

Author: markcoletti

pyproject.toml

@@ -45,11 +45,13 @@ dependencies = [
     "dask",
     #"dask==2022.10.0",
     #"dask==2023.12.1", # TODO need a version compatible with 3.8
-    "distributed",
+    "distributed"
 ]
 
 [project.optional-dependencies]
-docs = ["sphinx", "sphinx_rtd_theme"]
+# sphinx for making docs locally; matplotlib because some of the
+# examples generate figures.
+docs = ["sphinx", "sphinx_rtd_theme", "matplotlib"]
 
 [project.scripts]
 "ips.py" = "ipsframework.ips:main"