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I am trying to create a custom function in a Neural Network. The output of the NN is a n x 2 matrix which represent coordinates of points in a plane. From this, the Euclidean pairwise distance matrix needs to be computed which is then compared with the target pairwise distance matrix. Here is what I have so far:

coords1 = N@ Round[RandomReal[{-10., 10}, {5, 2}], 10^-4];

distM = Table[Table[EuclideanDistance[pi, pj], {pj, coords1}], {pi, coords1}] // MatrixForm; (* Distance Matrix *)

 (* Pure function that computes the distance matrix *)
func = (Partition[#, Sqrt@Length@#] &)@*
           Map[EuclideanDistance[#[[1]], #[[2]]] &]@*
            (Partition[Part[#, Join @@ Tuples[{Range@Length@#, Range@Length@#}]], 2] &

 (* The last Linear Layer 5 x 5 should be replaced by a layer that uses the above custom function to compute the distance matrix *)
net = NetChain[{LinearLayer[{5, 2}], ElementwiseLayer[Ramp], LinearLayer[{5, 5}]}, "Input" -> {5, 2}, "Output" -> {5, 5} ]

Any ideas? I have reviewed the documentation and I could not find anything that I could use. I appreciate any help in this matter.

Thanks

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  • $\begingroup$ What have you tried so far? Are you trying to define a single layer to perform all of these steps? $\endgroup$ Commented Aug 10, 2020 at 8:28

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I was able to solve the problem that I had using the following code:

    net2 = NetGraph[{PartLayer[{All, 1}], PartLayer[{All, 2}], 
                     ReplicateLayer[5, 1], ReplicateLayer[5, 2], 
                     ReplicateLayer[5, 1], ReplicateLayer[5, 2],   
                     ThreadingLayer[Subtract], ThreadingLayer[Subtract],  
                     ThreadingLayer[#^2 &], 
                     ThreadingLayer[#^2 &], ThreadingLayer[Plus], 
                     ThreadingLayer[Sqrt[#] &]}, 
                     { 1 -> 3, 2 -> 5, 1 -> 4, 2 -> 6, {3, 4} -> 7, 
                      {5, 6} -> 8, 7 -> 9, 8 -> 10, {9, 10} -> 11, 11 -> 12}];

net2[coords1] // MatrixForm
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