Consider the following adjacency matrix of a complete graph: $$A=(e^{-|i-j|})_{1\leq i\neq j\leq n}$$ with 0 on the diagonal. Let $D=diag\{d_1,...,d_n\}$ be the degree matrix where $d_i=\sum_{j\neq i}e^{-|i-j|}$. Then $L=D-A$ is the Laplacian. Let $L^\dagger$ be the Moore-Penrose inverse of the Laplacian. I'm interested in the following quantity $$a_{ij}=|(e_1-e_2)^TL^\dagger(e_i-e_j)|$$ where $e_i=(0,0...,0,1,0,...0)$ with 1 on the ith coordinate. I conjecture that $a_{ij}$ will decay exponentially when both $i$ and $j$ moves away from 1 and 2. Something like $a_{ij}\leq C _1e^{-C_2\min\{i,j\}}$ where $C_1,C_2$ are some constants. From the physics point of view, $a_{ij}$ is the voltage potential difference between $i$ and $j$. It is intuitive that when they are far away from the source, 1 and 2, they should be very small given the structure of the graph.

In fact, my simulation shows that as long as $i,j\neq1,2$, $a_{ij}$ suddenly becomes extremely close to 0. There seems to be no decay, but an acute cut. This phenomenon holds for slight perturbation of $A$, keeping the decaying property.

Is this conjecture true? How can we prove it? What is the rate of decay?

Another quantity that is also interesting is $$\sum_{i\neq j}e^{-|i-j|}a_{ij}$$ which is the weighted average of potential differences. How can we bound this? For this quantity, I conjecture it is bounded by some constant instead of growing with $n$. The physical meaning of this quantity is the sum of all currents in each edge.

(Update)

Enlightened by the discussion with @Abdelmalek Abdesselam below. We have the Neuman series representation: $$a_{ij}=|(e_1-e_2)^TD^{-1/2}\sum_{k\geq0}\left(D^{-1/2}AD^{-1/2}-\alpha D^{1/2}JD^{1/2}\right)^kD^{-1/2}(e_i-e_j)|$$ where $J$ is the matrix of all 1s and $\alpha$ is some constant to be chosen. We want to choose $\alpha$ such that the power of the matrix decays fast. How can we achieve this and bound the entries of $D^{-1/2}AD^{-1/2}-\alpha D^{1/2}JD^{1/2}$? A possible choice is $\alpha=1/tr(D)$.

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