2019-06-11 10:54:34 +0100 | asked a question | fractional chromatic index of edge-weighted graphs How would you compute the fractional chromatic index of an edge-weighted graph using SAGE? The built-in function fractional_chromatic_index seems to compute the fractional chromatic index for only unweighted graphs. For instance, if $G$ is the 5-cycle graph, its fractional chromatic index is $2.5$. But if one of the edges can be ignored, say by giving it a zero weight, then the fractional chromatic index becomes $2$. The code and output below shows that SAGE ignores the edge-weights (notice that the edge-weights need not be integral - in the graph below, the correct value of the fractional chromatic index is 2.1, which is the maximum sum $1.1+1.0$ of weights of edges incident to a vertex): Is there some way to get the built-in function to take edge weights into account? Or can this value be computed using some other method? |
2015-01-01 06:01:58 +0100 | received badge | ● Editor (source) |
2014-12-31 11:59:27 +0100 | asked a question | permission settings in SAGE installation in ubuntu My sage installation doesn't seem to work properly on a couple issues and I believe these are related to file permissions. Let me be specific. I downloaded the SAGE .tar.lzma file and installed it in the /opt directory (in Ubuntu 14). The first problem is that to launch sage, I need to type "sudo sage" because typing "sage" alone at the terminal gives the following error message:
So I type "sudo sage" and get into the sage prompt. At this point, the "load filename.sage" command doesn't work (this is the second problem with the installation). For example, loading a simple file test1.sage (which just does "x=3; print x+1") gives the following error message:
At another time, I got the response the load command was not found:
I think the permissions on some of the files need to be changed from root to my username. I didn't have this problem earlier when I used the previous version of SAGE with Ubuntu 12, and I'm wondering if I did something wrong in the installation process. |