Pairwise L2 distances in Torch

pdist.lua

-- A is a matrix n x d, B is a matrix m x d, i.e. data points are row vectors; returns a matrix n x m
function pdist(A, B)
    local eps = 1e-6
    local pdist2 = A * B:t()
    local normA = torch.sum(torch.cmul(A, A), 2):view(pdist2:size(1), 1):expandAs(pdist2)
    local normB = torch.sum(torch.cmul(B, B), 2):t():view(1, pdist2:size(2)):expandAs(pdist2)
    return torch.sqrt(normA - 2.0 * pdist2 + normB + eps)
end