Simultaneous Nearest Neighbor Search Piotr Indyk Robert Kleinberg MIT Cornell Sepideh Mahabadi Yang Yuan MIT Cornell
Nearest Neighbor β’ Dataset of π points π in a metric space (π, π π ) 6/17/2016 2
Nearest Neighbor β’ Dataset of π points π in a metric space (π, π π ) β’ A query point comes online π π 6/17/2016 3
Nearest Neighbor β’ Dataset of π points π in a metric space (π, π π ) β’ A query point comes online π π β’ Goal: π β β’ Find the nearest data-set point π β 6/17/2016 4
Nearest Neighbor β’ Dataset of π points π in a metric space (π, π π ) β’ A query point comes online π π β’ Goal: π β β’ Find the nearest data-set point π β β’ Do it in sub-linear time 6/17/2016 5
Approximate Nearest Neighbor β’ Dataset of π points π in a metric space (π, π π ) β’ A query point comes online π π π β’ Goal: π β β’ Find the nearest data-set point π β β’ Do it in sub-linear time β’ Approximate Nearest Neighbor 6/17/2016 6
What if We have multiple queries We need the results of the queries to be related. 6/17/2016 7
What if We have multiple queries We need the results of the queries to be related. Example: β’ Noisy image β’ For each pixel find the true color β’ Neighboring pixels have similar color 6/17/2016 8
Simultaneous NN Problem 6/17/2016 Sepideh Mahabadi 9
The SNN problem ( Felzenszwalbβ15) β’ Dataset of π points π in a metric space (π, π π ) 6/17/2016 10
The SNN problem ( Felzenszwalbβ15) β’ Dataset of π points π in a metric space (π, π π ) β’ Query comes online and contains π 2 β’ π query points π = (π 1 , β¦ , π π ) π 3 π 1 6/17/2016 11
The SNN problem ( Felzenszwalbβ15) β’ Dataset of π points π in a metric space (π, π π ) β’ Query comes online and contains π 2 β’ π query points π = (π 1 , β¦ , π π ) π 3 π 1 β’ A compatibility graph π» = π , πΉ π» 6/17/2016 12
The SNN problem ( Felzenszwalbβ15) β’ Dataset of π points π in a metric space (π, π π ) β’ Query comes online and contains π 2 β’ π query points π = (π 1 , β¦ , π π ) π 3 π 1 β’ A compatibility graph π» = π , πΉ π» 6/17/2016 13
The SNN problem (Felzenszwalbβ15) β’ Dataset of π points π in a metric space (π, π π ) β’ Query comes online and contains π 2 β’ π query points π = (π 1 , β¦ , π π ) π 3 π 1 β’ A compatibility graph π» = π , πΉ π» 6/17/2016 14
The SNN problem ( Felzenszwalbβ15) β’ Dataset of π points π in a metric space (π, π π ) π 3 β’ Query comes online and contains π 2 π 2 β’ π query points π = (π 1 , β¦ , π π ) π 3 π 1 π 1 β’ A compatibility graph π» = π , πΉ π» β’ Goal is to report (π 1 , β¦ , π π ) , π π β π , that minimizes π π=π π π (π π , π π ) + π π ,π π βπ π― π π (π π , π π ) 6/17/2016 15
The Generalized SNN β’ Dataset of π points π in a metric space (π, π π ) π 3 β’ Query comes online and contains π 2 π 2 β’ π query points π = (π 1 , β¦ , π π ) π 3 π 1 π 1 β’ A compatibility graph π» = π , πΉ π» β’ Goal is to report (π 1 , β¦ , π π ) , π π β π , that minimizes π π=π π π π π (π π , π π ) + π π ,π π βπ π― π π,π π π (π π , π π ) 6/17/2016 16
Independent NN Algorithm 6/17/2016 Sepideh Mahabadi 17
Independent NN Algorithm INN Algorithm β’ For each query point π π β π π 2 π 3 π 1 6/17/2016 18
Independent NN Algorithm INN Algorithm β’ For each query point π π β π β’ Independently find a (approximate) nearest neighbor π π (Searching step) π 2 π 2 π 3 π 1 π 1 π 3 6/17/2016 19
Independent NN Algorithm INN Algorithm β’ For each query point π π β π β’ Independently find a (approximate) nearest neighbor π π (Searching step) β’ Replace the label set π with the reduced set πΈ = { π π , β¦ , π π } (Pruning step) π 2 π 2 π 3 π 1 π 1 π 3 6/17/2016 20
Independent NN Algorithm INN Algorithm β’ For each query point π π β π β’ Independently find a (approximate) nearest neighbor π π (Searching step) β’ Replace the label set π with the reduced set πΈ = { π π , β¦ , π π } (Pruning step) β’ Solve the problem for π π 2 π 2 π 3 π 1 π 1 π 3 6/17/2016 21
Independent NN Algorithm INN Algorithm β’ For each query point π π β π β’ Independently find a (approximate) nearest neighbor π π (Searching step) β’ Replace the label set π with the reduced set πΈ = { π π , β¦ , π π } (Pruning step) β’ Solve the problem for π π 2 π 2 ο Reduces the size of labels from π down to π π 3 π 1 π 1 π 3 6/17/2016 22
Independent NN Algorithm INN Algorithm β’ For each query point π π β π β’ Independently find a (approximate) nearest neighbor π π (Searching step) β’ Replace the label set π with the reduced set πΈ = { π π , β¦ , π π } (Pruning step) β’ Solve the problem for π π 2 π 2 ο Reduces the size of labels from π down to π π 3 π 1 π 1 π 3 ο The optimal value increases by a factor π· ο pruning gap 6/17/2016 23
Independent NN Algorithm INN Algorithm β’ For each query point π π β π β’ Independently find a (approximate) nearest neighbor π π (Searching step) β’ Replace the label set π with the reduced set πΈ = { π π , β¦ , π π } (Pruning step) β’ Solve the problem for π π 2 π 2 ο Reduces the size of labels from π down to π π 3 π 1 π 1 π 3 ο The optimal value increases by a factor π· ο pruning gap ο Any metric labeling πΎ -approximate algorithm can be used on the reduced set , giving us (π½ β πΎ) -approximate algorithm. 6/17/2016 24
Results 6/17/2016 Sepideh Mahabadi 25
Results β’ Prove bounds for the pruning gap 6/17/2016 26
Results β’ Prove bounds for the pruning gap π¦π©π‘ π β’ π· = π· π¦π©π‘ π¦π©π‘ π₯ 6/17/2016 27
Results β’ Prove bounds for the pruning gap π¦π©π‘ π β’ π· = π· π¦π©π‘ π¦π©π‘ π₯ β’ π· = π π¦π©π‘ π 6/17/2016 28
Results β’ Prove bounds for the pruning gap π¦π©π‘ π β’ π· = π· π¦π©π‘ π¦π©π‘ π₯ β’ π· = π π¦π©π‘ π β’ For π -sparse graph: π· = π· π 6/17/2016 29
Results β’ Prove bounds for the pruning gap π¦π©π‘ π β’ π· = π· π¦π©π‘ π¦π©π‘ π₯ β’ π· = π π¦π©π‘ π β’ For π -sparse graph: π· = π· π β’ Graphs with pseudo-arboricity π : each edge can be mapped to a vertex such that at most π edges are mapped to any vertex 6/17/2016 30
Results β’ Prove bounds for the pruning gap π¦π©π‘ π β’ π· = π· π¦π©π‘ π¦π©π‘ π₯ β’ π· = π π¦π©π‘ π β’ For π -sparse graph: π· = π· π β’ Graphs with pseudo-arboricity π : each edge can be mapped to a vertex such that at most π edges are mapped to any vertex β’ Would mean constant approximation factor for trees, grids, planar graphs , β¦, and in particular π(π ) -approximation for π - degree graphs 6/17/2016 31
Results β’ Prove bounds for the pruning gap π¦π©π‘ π β’ π· = π· π¦π©π‘ π¦π©π‘ π₯ β’ π· = π π¦π©π‘ π β’ For π -sparse graph: π· = π· π β’ Graphs with pseudo-arboricity π : each edge can be mapped to a vertex such that at most π edges are mapped to any vertex β’ Would mean constant approximation factor for trees, grids, planar graphs , β¦, and in particular π(π ) -approximation for π - degree graphs β’ π· is very close to one in experiments 6/17/2016 32
Results β’ Prove bounds for the pruning gap π¦π©π‘ π β’ π· = π· π¦π©π‘ π¦π©π‘ π₯ β’ π· = π π¦π©π‘ π β’ For π -sparse graph: π· = π· π β’ Graphs with pseudo-arboricity π : each edge can be mapped to a vertex such that at most π edges are mapped to any vertex β’ Would mean constant approximation factor for trees, grids, planar graphs , β¦, and in particular π(π ) -approximation for π - degree graphs β’ π· is very close to one in experiments 6/17/2016 33
Overview of the proof for π¦π©π‘ π π· = π· π¦π©π‘ π¦π©π‘ π 6/17/2016 Sepideh Mahabadi 34
0-Extension Problem [Kar98] 6/17/2016 35
0-Extension Problem [Kar98] β’ The input: β’ a graph πΌ π, πΉ 6/17/2016 36
0-Extension Problem [Kar98] β’ The input: β’ a graph πΌ π, πΉ β’ a weight function π₯ π 1 2 2 1 2 6/17/2016 37
0-Extension Problem [Kar98] β’ The input: β’ a graph πΌ π, πΉ β’ a weight function π₯ π β’ a set of terminals π β π 1 2 2 1 2 6/17/2016 38
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