Revision #2 Authors: Roee David, Elazar Goldenberg, Robert Krauthgamer

Accepted on: 2nd April 2017 12:16

Downloads: 117

Keywords:

We study the problem of \emph{reconstructing a low-rank matrix}, where the input is an $n\times m$ matrix $M$ over a field $\mathbb{F}$ and the goal is to reconstruct a (near-optimal) matrix $M'$ that is low-rank and close to $M$ under some distance function $\Delta$.

Furthermore, the reconstruction must be local, i.e., provides access to any desired entry of $M'$ by reading only a few entries of the input $M$ (ideally, independent of the matrix dimensions $n$ and $m$).

Our formulation of this problem is inspired by the local reconstruction framework of Saks and Seshadhri (SICOMP, 2010).

Our main result is a local reconstruction algorithm for the case where $\Delta$ is the normalized Hamming distance (between matrices).

Given $M$ that is $\epsilon$-close to a matrix of rank $d<1/\epsilon$ (together with $d$ and $\epsilon$), this algorithm computes with high probability a rank-$d$ matrix $M'$ that is $O(\sqrt{d\epsilon})$-close to $M$.

This is a local algorithm that proceeds in two phases.

The \emph{preprocessing phase} reads only $O(\sqrt{{d}/{\epsilon^3}})$ random entries of $M$,

and stores a small data structure.

The \emph{query phase} deterministically outputs a desired entry $M'_{i,j}$ by reading only the data structure and $2d$ additional entries of $M$.

We also consider local reconstruction in an easier setting, where the algorithm can read an entire matrix column in a single operation. When $\Delta$ is the normalized Hamming distance between vectors,

we derive an algorithm that runs in polynomial time

by applying our main result for matrix reconstruction.

For comparison, when $\Delta$ is the truncated Euclidean distance and $\mathbb{F}=\mathbb{R}$,

we analyze sampling algorithms by using statistical learning tools.

Fixed several bugs in the proof Appeared on Section 4.

Revision #1 Authors: Roee David, Elazar Goldenberg, Robert Krauthgamer

Accepted on: 27th December 2015 15:14

Downloads: 453

Keywords:

We study the problem of \emph{reconstructing a low-rank matrix}, where the input is an $n\times m$ matrix $M$ over a field $\F$

and the goal is to reconstruct a (near-optimal) matrix $M'$

that is low-rank and close to $M$ under some distance function $\Delta$.

Furthermore, the reconstruction must be local, i.e., provides access to

any desired entry of $M'$ by reading only a few entries of the input $M$

(ideally, independent of the matrix dimensions $n$ and $m$).

Our formulation of this problem is inspired by the local reconstruction framework of Saks and Seshadhri (SICOMP, 2010).

Our main result is a local reconstruction algorithm for the case

where $\Delta$ is the normalized Hamming distance (between matrices).

Given $M$ that is $\epsilon$-close to a matrix of rank $d<1/\epsilon$

(together with $d$ and $\epsilon$),

this algorithm computes with high probability a rank-$d$ matrix $M'$

that is $O(\sqrt{d\epsilon})$-close to $M$.

This is a local algorithm that proceeds in two phases.

The \emph{preprocessing phase}

reads only $\tO(\sqrt{{d}/{\epsilon^3}})$ random entries of $M$,

%runs in time $\tO\big( \frac{1}{\epsilon} (\frac{(8e)^2\ln^2 d}{ d\epsilon })^{d} \big)$

and stores a small data structure.

The \emph{query phase} deterministically outputs a desired entry $M'_{i,j}$

by reading only the data structure and $2d$ additional entries of $M$.

% runs in time $O(d^2)$

We also consider local reconstruction in an easier setting,

where the algorithm can read an entire matrix column in a single operation.

When $\Delta$ is the normalized Hamming distance between vectors,

we derive an algorithm that runs in polynomial time

by applying our main result for matrix reconstruction.

For comparison, when $\Delta$ is the truncated Euclidean distance and $\F=\R$,

we analyze sampling algorithms by using statistical learning tools.

TR15-128 Authors: Roee David, Elazar Goldenberg, Robert Krauthgamer

Publication: 10th August 2015 11:15

Downloads: 496

Keywords:

We study the problem of \emph{reconstructing a low-rank matrix}, where the input is an $n\times m$ matrix $M$ over a field $\mathbb{F}$ and the goal is to reconstruct a (near-optimal) matrix $M'$ that is low-rank and close to $M$ under some distance function $\Delta$.

Furthermore, the reconstruction must be local, i.e., provides access to any desired entry of $M'$ by reading only a few entries of the input $M$ (ideally, independent of the matrix dimensions $n$ and $m$).

Our formulation of this problem is inspired by the local reconstruction framework of Saks and Seshadhri (SICOMP, 2010).

Our main result is a local reconstruction algorithm for the case where $\Delta$ is the normalized Hamming distance (between matrices).

Given $M$ that is $\epsilon$-close to a matrix of rank $d<1/\epsilon$ (together with $d$ and $\epsilon$), this algorithm computes with high probability a rank-$d$ matrix $M'$ that is $O(\sqrt{d\epsilon})$-close to $M$.

This is a local algorithm that proceeds in two phases.

The \emph{preprocessing phase} reads only $O(\sqrt{{d}/{\epsilon^3}})$ random entries of $M$,

and stores a small data structure.

The \emph{query phase} deterministically outputs a desired entry $M'_{i,j}$ by reading only the data structure and $2d$ additional entries of $M$.

We also consider local reconstruction in an easier setting, where the algorithm can read an entire matrix column in a single operation. When $\Delta$ is the normalized Hamming distance between vectors,

we derive an algorithm that runs in polynomial time

by applying our main result for matrix reconstruction.

For comparison, when $\Delta$ is the truncated Euclidean distance and $\mathbb{F}=\mathbb{R}$,

we analyze sampling algorithms by using statistical learning tools.