udisomapgeodistancek.m

提供了一种维数约减的思路

function [GeoD,D]=udIsomapGeoDistanceK(X, NeighborsNum); 

% 计算Isomap算法的测地线距离
% Input:
%    X = D x N matrix of input points (where D is the dimensionality of points, N is the number of data points)
%    NeighborsNum = neighborhood size
%
% Output: 
%    GeoD = Geodesic Distance

%%%%% Step 0: Initialization and Parameters %%%%%

D = L2_distance(X, X, 1);

N = size(D,1); 
if ~(N==size(D,2))
   error('D must be a square matrix'); 
end; 

K = NeighborsNum; 

INF =  1000*max(max(D))*N;  %% effectively infinite distance

%%%%% Step 1: Construct neighborhood graph %%%%%
%disp('Constructing neighborhood graph...'); 

[tmp, ind] = sort(D); 
tic; 
for i=1:N
   D(i,ind((2+K):end,i)) = INF; 
end

D = sparse(D);
D = min(D,D');    %% Make sure distance matrix is symmetric


%%%% Step 2: Compute shortest paths %%%%%
landmarks = 1:N;
GeoD = dijkstra(sparse(D), landmarks);
return;