Lovasz' theta function used to work. Now it is broken for a wide variety of graphs. Here's one example:
In this case the produced error is:
Error in lines 2-2
Traceback (most recent call last):
File "/cocalc/lib/python3.8/site-packages/smc_sagews/sage_server.py", line 1230, in execute
File "", line 1, in <module>
File "/ext/sage/sage-9.3/local/lib/python3.9/site-packages/sage/graphs/lovasz_theta.py", line 76, in lovasz_theta
ValueError: could not convert string to float: b'failed.'