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Calculate distance matrix
Posted:
Jun 4, 2013 7:51 AM


Hi everybody,
I hope you will have the right answer to this question, which is rather challanging.
I have two unidimensional vectors Y and Z, which hold the coordinates of N grid points located on a square grid. So
Ny points along Y Nz points along Z N = Ny*Nz Y = Y[N]; (Y holds N entries) Z = Z[N]; (Z holds N entries)
Now, the goal would be generating the distance matriy D, which holds N*N entries: so each row of matrix D is defined as the distance between the ith point on the grid and the remnant (N  i) points.
Generally, to compute the whole matrix I would call
D = squareform(pdist([Y Z])); or,equivalently, D = pdist2([Y Z],[Y Z]).
But, since D is a square matrix, I'd like to generate only the N(N + 1)/2 independent entries and store them into a unidimensional vector Dd.
So the question is: how to generate a unidimensional array Dd whose entries are the defined by the lower traingular terms of matrix D? I'd, furthermore, like storing the entries in a columnmajor order.
I hope the explanation is clear enough.
Thanks in advance, Fpe



