Graph class method .lovasz_theta is broken

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Craig E Larson

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Jul 19, 2021, 3:39:41 PMJul 19
to sage-support
Lovasz' theta function used to work. Now it is broken for a wide variety of graphs. Here's one example:

g=graphs.CompleteGraph(20)
g.lovasz_theta()

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 exec( 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 return float(lines.split()[-1]) ValueError: could not convert string to float: b'failed.'

David Joyner

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Jul 19, 2021, 5:17:51 PMJul 19
to SAGE support
On Mon, Jul 19, 2021 at 3:39 PM Craig E Larson <cla...@vcu.edu> wrote:
Lovasz' theta function used to work. Now it is broken for a wide variety of graphs. Here's one example:

g=graphs.CompleteGraph(20)
g.lovasz_theta()


Using sage-9.1.rc5 (after installing csdp):

sage: g=graphs.CompleteGraph(20)
sage: g.lovasz_theta()
1.0


 
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 exec( 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 return float(lines.split()[-1]) ValueError: could not convert string to float: b'failed.'

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