fieldofnodes's profile - activity

So I had this working, but had to change computers. Now I get this error:

TypeError: the optional plantri package is not installed

Then when I try sage -i plantri in

jonathan@Field-Phys-Math ~/SageMath $ sage -i plantri
make: *** No rule to make target 'all-toolchain'.  Stop.

My version is SageMath version 7.5.1, Release Date: 2017-01-15

What is the deal?

So here is my code:

import sage.graphs.generic_graph

class NewGraph(Graph): def is_apex(self): not_apex = False for v in self.vertex_iterator(): l = self.neighbors(v) g.delete_vertex(v) if self.is_planar(): return True self.add_vertex(v) self.add_edges([(v, y) for y in l]) return False

This is the result:

k6=graphs.CompleteGraph(6)

sage: k6.is_apex()

AttributeError Traceback (most recent call last) <ipython-input-3-e18df0843618> in <module>() ----> 1 k6.is_apex()

AttributeError: 'Graph' object has no attribute 'is_apex'

What is happening?

I am unfamiliar with the details of the "Graph" class need to know where to go to look for more info. Help?

I would like to use patches in my sagemath scripts, along with certain library imports - as one does in python - but I am finding it hard to learn how to do this.

Can anyone assist in this regards?

Thank you, I am using that right now, it is definitely helpful.

I am very new to Sage, how would I use this in, say the terminal?

I am interested in creating a web-app that allows for graph creation, edge contraction, vertex splits, and then exports to sage.

If anyone knows of something like this already developed please let me know, otherwise any suggestions on how to begin?

Thanks

Hi,

Sage has the command:

hamiltonian_cycle(algorithm='tsp')

"Returns a Hamiltonian cycle/circuit of the current graph/digraph A graph (resp. digraph) is said to be Hamiltonian if it contains as a subgraph a cycle (resp. a circuit) going through all the >vertices. Computing a Hamiltonian cycle/circuit being NP-Complete, this algorithm could run for some time depending on the instance.

ALGORITHM:

See Graph.traveling_salesman_problem for ‘tsp’ algorithm and find_hamiltonian from sage.graphs.generic_graph_pyx for >>‘backtrack’ algorithm.

INPUT:

algorithm - one of ‘tsp’ or ‘backtrack’. OUTPUT: If using the ‘tsp’ algorithm, returns a Hamiltonian cycle/circuit if it exists; otherwise, raises a EmptySetError exception. If >>using the ‘backtrack’ algorithm, returns a pair (B,P). If B is True then P is a Hamiltonian cycle and if B is False, P is a >>longest path found by the algorithm. Observe that if B is False, the graph may still be Hamiltonian. The ‘backtrack’ >>algorithm is only implemented for undirected graphs."

The above is directly from Hamiltonian Cycle

Added in the same area on the page is:

sage: g = graphs.HeawoodGraph()
sage: g.hamiltonian_cycle()
TSP from Heawood graph: Graph on 14 vertices
sage: g = graphs.PetersenGraph()
sage: g.hamiltonian_cycle()
Traceback (most recent call last):
...
EmptySetError: The given graph is not Hamiltonian

So clearly there is some algorithms on your question, though it is also known that this is an NP-Complete problem.

Good luck, fieldofnodes

Hi,

I am researching methods that relate to graph minors. Currently I am looking at creating a method/function/attribute (I give the options as I do not know the best means, . . . , yet) which will allow me to test for forbidden minors.

An example is the complete graph on 6 vertices is a forbidden minor for the class of graphs that are not apex. Meaning, that given a graph G and a $v\in V(G)$, that $G-v$ is not planar. So the code that I have been working on should test if a graph matches a certain criteria. I would be able to ask SageMath in the following way

K6=graphs.CompleteGraph(6); K6.is_apex()

Of which the response would be

False

This is the code that I have been working on

def is_apex(g):
for v in g.vertex_iterator():
    l = g.neighbors(v)
    g.delete_vertex(v)
    if g.is_planar():
        return True
    g.add_vertex(v)
    g.add_edges([(v, y) for y in l])
return False

Now I had help on this from another member in the AskSage community, so thank you.

But now I am trying to do something like this:

class Graph():
not_apex = False
def is_apex(self):
    for v in self.vertex_iterator():
        l = self.neighbors(v)
        g.delete_vertex(v)
        if self.is_planar():
            return True
        self.add_vertex(v)
        self.add_edges([(v, y) for y in l])
    return False

Which when I enter

x.is_apex()

Of which the response that I get

---------------------------------------------------------------------------

AttributeError Traceback (most recent call last) <ipython-input-15-e74e0334c694> in <module>() ----> 1 x.is_apex()

AttributeError: 'Graph' object has no attribute 'is_apex'

I am still a nooooooooob, so any help in understanding what I need to do would be great.

Thank you

Great mate. This is very much in the direction that I am heading. I really appreciate the comment.

I am working on topological graph theory problems and using SageMath. I want to create a function that give a boolean True or False answer, so I can use this answer for further use. My current function that I use:

def is_apex(a):
for v in a.vertex_iterator():
    l=a.neighbors(v)
    if a.is_planar(a.delete_vertex(v)):
        print("Deleting vertex ",v," makes a planar graph")
        a.add_vertex(v)
        a.add_edges([(v, y) for y in l])
    else:
        a.add_vertex(v)
        a.add_edges([(v, y) for y in l])
        print("Deleting vertex ",v," does not make a planar graph")

I am a noob when it comes to programming, and any help would be awesome.

I want a True returned if the graph is apex and a False value to return for not apex.

Thoughts?

EXCELLENT!!! I did what you said, works great.

I am using sagemath -7.3 and I have recently added the package "plantri-4.5" to my packages.

I want to generate all planar graphs that have connectivity (κ=3). I want to have an initial graph G0 with 4 vertices, which we know is the complete graph on 4 vertices (K_4).

Then, I want all planar graphs on 4 vertices that is 3−connected.

Then, I want all planar graphs on 5 vertices that is 3−connected.

Than, I want all planar graphs on 6 vertices that is 3−connected.

I would like to ensure that I am actually obtaining ALL graphs that have the above criteria.

My goal is to obtain up to n=15,all planar graphs of connectivity, κ=3. I mean of course vertex connectivity as well.

I have been looking at Plantri as a way to do this, as they claim to have this ability.

Though I am having issues actually using this program within the sage terminal (Linux: Ubuntu base with cinnamon 16.0).

Does anyone have any suggestions on how to use plantri in the sage environment?