In my network, beside to the information of which two nodes create an edge, I have the information of the time duration which an edge has lasted. I included this information as weight and used them as the covariate of the SBM. The results seems more reasonable compared to not considering any weights. However, the number of blocks changes slightly in each time I ran my script with the piece of code given before. So I was wondering if I must run minimize_nested_blockmodel_dl function by determining the higher number of MCMC iterations as argument, and then I would get more accurate results with highest confidence interval or I just need to repeat this function in a loop and then compute the mean number of blocks? I hope my question makes sense.

Thanks again. Zahra

On Thu, Apr 26, 2018 at 3:43 PM, Tiago de Paula Peixoto tiago@skewed.de wrote:

On 26.04.2018 12:52, Zahra Sheikhbahaee wrote:

...

Hi there,

I am trying to include the edge weights by taking to account an edge

covariate matrix for the nested block model inference. Well, Each time I run the code on my data set I get slightly different results both in terms of number of blocks and the nodes in each block.

This is because the inference is made using MCMC, which is a stochastic algorithm. You have to run it multiple times, and select the result with largest posterior probability (if you only want a point estimate).

...

This is my code: state = minimize_nested_blockmodel_dl(g, state_args=dict(recs=[g.edge_properties["weight"]],

rec_types=["discrete-geometric"]))

...

state.draw(edge_color=prop_to_size(g.edge_properties["weight"],

power=1, log=True),

...

           ecmap=(matplotlib.cm.gist_heat, .6),
           eorder=g.edge_properties["weight"],
           edge_pen_width=prop_to_size(g.edge_properties["weight"],

1, 4, power=1, log=True),

...

           edge_gradient=[],
           vertex_text=g.vertex_properties["attribute"],
           vertex_text_position="centered",
           vertex_text_rotation=g.vertex_properties['text_rotation'],

...

           vertex_font_size=10,
           vertex_font_family='mono',
           vertex_anchor=0,
           output_size=[1024*2,1024*2],
           output="DiscreteGeometric_%s.pdf"%(eventName))

Although it not important for the questions you have raised, it is not very useful to post incomplete code. Normally, for troubleshooting purposes, it is necessary for you to provide a _minimal_ and _self-contained_ program that anyone could execute and verify the problem you are reporting.

...

I appreciate if you explain what your approach would be and how I can run graph-tool using the covariance matrix of edges in order to get statistically reliable results?

This is covered in detail in the HOWTO:

https://graph-tool.skewed.de/static/doc/demos/inference/inference.html

and also in many papers, e.g.

https://arxiv.org/abs/1705.10225 https://arxiv.org/abs/1708.01432

However, I'm note sure what you mean by "covariance matrix of edges". The approach in question deals with graphs with edge covariates (a.k.a. weights). A covariance matrix usually refers to something else.

...

Is there also any way to get the full posterior of each node belonging to each block?

This is also explained in detail in the HOWTO:

https://graph-tool.skewed.de/static/doc/demos/inference/ inference.html#sampling-from-the-posterior-distribution

Best, Tiago

-- Tiago de Paula Peixoto tiago@skewed.de _______________________________________________ graph-tool mailing list graph-tool@skewed.de https://lists.skewed.de/mailman/listinfo/graph-tool

Thanks a lot for the advice!

On Thu, Apr 26, 2018 at 5:26 PM, Tiago de Paula Peixoto tiago@skewed.de wrote:

On 26.04.2018 15:29, Zahra Sheikhbahaee wrote:

...

In my network, beside to the information of which two nodes create an

edge,

...

I have the information of the time duration which an edge has lasted. I included this information as weight and used them as the covariate of the SBM. The results seems more reasonable compared to not

considering

...

any weights. However, the number of blocks changes slightly in each time

I

...

ran my script with the piece of code given before. So I was wondering if

I

...

must run minimize_nested_blockmodel_dl function by determining the higher number of MCMC iterations as argument, and then I would get more accurate results with highest confidence interval or I just need to repeat this function in a loop and then compute the mean number of blocks? I hope my question makes sense.

You should run the algorithm multiple times, and choose the result with the smallest description length. You get this value via the method state.entropy().

Best, Tiago

-- Tiago de Paula Peixoto tiago@skewed.de _______________________________________________ graph-tool mailing list graph-tool@skewed.de https://lists.skewed.de/mailman/listinfo/graph-tool

Am 16.07.2018 um 15:15 schrieb Zahra Sheikhbahaee:

For the non-parametric weighted SBMs, how can I extract the "description length" from the the state.entropy() method? Is it also equivalent of having the maximum entropy values after running the algorithm multiple times ?

The entropy() method returns the negative joint log-likelihood of the data and model parameters. For discrete data and model parameters, this equals the description length.

For the weighted SBM with continuous covariates, the data and model are no longer discrete, so this value can no longer be called a description length, although it plays the same role. However, for discrete covariates, it is the description length.

I also have a theoretical question: I read most of your recent papers and I see this statement but I could not find more description why it is the case? Why do you use the "micro-canonical formulation"? You stated that "it approaches to the canonical distributions asymptotically". In case you have explained it in one of your papers, would you kindly refer me to the right paper?

The microcanonical model is identical to the canonical model, if the latter is integrated over its continuous parameters using uninformative priors, as explained in detail here:

https://arxiv.org/abs/1705.10225

Therefore, in a Bayesian setting, it makes no difference which one is used, as they yield the same posterior distribution.

The main reason to use the microcanonical formulation is that it makes it easier to extend the Bayesian hierarchy, i.e. include deeper priors and hyperpriors, thus achieving more robust models without a resolution limit, accepting of arbitrary group sizes and degree distributions, etc. Within the canonical formulation, this is technically more difficult.

Best, Tiago

Am 16.07.2018 um 22:46 schrieb Zahra Sheikhbahaee:

Hi Tiago,

Thanks for the explanation. I have another question:

In the "Inferring the mesoscale structure of layered, edge-valued and time-varying networks", you compared two way of constructing layered structures: first approach: You assumed an adjacency matrix in each independent layer. The second method, the collapsed graph considered as a result of merging all the adjacency matrices together.

I am wondering how I can use graph_tool for the first method? Which method or class should I use?

You have to pass the option "layers=True" to the LayeredBlockState constructor:

https://graph-tool.skewed.de/static/doc/inference.html#graph_tool.inference....

If there is a class, is it still possible to consider a graph with weighted edges?

Yes, it accepts 'recs/rec_types/rec_params' just like the regular BlockState.

Best, Tiago

Am 19.07.2018 um 16:01 schrieb Zahra Sheikhbahaee:

Thanks for the reply. In the section (VI) of your paper "Inferring the mesoscale structure of layered, edge-valued and time-varying networks", you used the layered stochastic block model for a temporal network. I have a similar data set which I do not want to fix the membership for the nodes of different layers to the same block over all layers (nodes can change their block memberships  over time). I am wondering again how I can use graph tool for this case?  Which method or constructor should I use?

It's always the same constructor, LayeredBlockState. To allow the membership to change across layers, you need to set overlap=True.

Am 19.07.2018 um 19:17 schrieb Zahra Sheikhbahaee:

I have another naive question: It is not still clear for me how I could pass different weighted graphs of each timestamp to this LayeredBlockState constructor while I want that each of these weighted graphs be considered as one layer of this multilayer network? Because the input is just a single graph.

Right, you have to collapse them in a single graph with multiple edges. The time-stamp on the edges (i.e. the "layers") should be stored as a property map that you pass as the 'ec' parameter to LayeredBlockState.