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# compute the adjacency matrix from the correlation

is there a formula to compute the adjacency matrix from the correlation matrix?

ASKER

Actually we can compute the adjacency matrix.

But as usual the problem is the threshold.

so what i did is the following:

if value[i,j] > 0.7 --> adj[i,j] = 0

else adj[i,j] = 1

but we go back to the problem of threshold selection, i just tried 0.7 it worked ok.

But as usual the problem is the threshold.

so what i did is the following:

if value[i,j] > 0.7 --> adj[i,j] = 0

else adj[i,j] = 1

but we go back to the problem of threshold selection, i just tried 0.7 it worked ok.

By "it worked ok" do you mean it gave the exact answer or that it got close? Is there complete separation or will you have some error no matter what threshold you choose?

Is this related to a previous question that explains what you are computing?

If there is no guarantee that you can correctly classify each cell in the matrix, then which is worse, false positives or false negatives?

Is this related to a previous question that explains what you are computing?

If there is no guarantee that you can correctly classify each cell in the matrix, then which is worse, false positives or false negatives?

ASKER

Sorry for being late i was very busy:

http://www.gipsa-lab.inpg.fr/~sophie.achard/brainwaver/choose.thresh.nbedges.html

Concerning this part of the question, i didn't really think about it. Can u give me an example on how to do it? but till now i am just picking a threshold manually.

Well it's a very hard problem to solve.

that's another link if u are interested: http://www.slideshare.net/athanasios/itab2010thresholding-correlation-matrices

The problem is that i don't have much time, but getting more ideas is really good to improve my classification.

Thank you,

By "it worked ok" do you mean it gave the exact answer or that it got close?, Is there complete separation or will you have some error no matter what threshold you choose?

Well it wont give me an exact question of course, since it's a threshold that i decided to choose, so i wont be able to have exact results. I will only have A VERY close result or close if the threshold is extracted from the Dataset with a specific method that i don't know how. If u know R-cran i'll send u a link for a function that do that:http://www.gipsa-lab.inpg.fr/~sophie.achard/brainwaver/choose.thresh.nbedges.html

If there is no guarantee that you can correctly classify each cell in the matrix, then which is worse, false positives or false negatives?

Concerning this part of the question, i didn't really think about it. Can u give me an example on how to do it? but till now i am just picking a threshold manually.

Well it's a very hard problem to solve.

that's another link if u are interested: http://www.slideshare.net/athanasios/itab2010thresholding-correlation-matrices

The problem is that i don't have much time, but getting more ideas is really good to improve my classification.

Thank you,

ASKER

I hope to keep the subject open, and keep u updated, or even if u have ideas it will be great.

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Is your adjacency matrix for a non-directed, unweighted graph? (all 0s and 1s and symmetrical about the main diagonal)

A correlation matrix usually shows how related things are. This will not give you what are directly connected.

My guess is the answer is no. I see no way that you could get an adjacency matrix from a correlation matrix; however, if you describe in more detail, perhaps we can help get the same result some other way.