MINBALL |
Minimal enclosing ball in kernel feature space.
Synopsis:
model = minball(X)
model = minball(X,options)
Description:
It computes center and radius of the minimal ball
enclosing data X mapped into a feature space induced
by a given kernel. The problem leads to a special instance
of the Quadratic Programming task which is solved by the
GMNP solver (see 'help gmnp').
Input:
X [dim x num_data] Input data.
options [struct] Control parameters:
.ker [string] Kernel identifier (default 'linear'). See 'help kernel'.
.arg [1 x nargs] Kernel arguments.
.solver [string] Solver to be used (see 'help gmnp'); default 'imdm';
.C [1x1] Regularization constant (default []); If C > 0 it is equivalent
to the Support Vector Data Description (or 1-class SVM) by Tax-Duin
with quadratric penalization of overlapping data.
Output:
model [struct] Center of the ball in the kernel feature space:
.sv.X [dim x nsv] Data determining the center.
.Alpha [nsv x 1] Data weights.
.r [1x1] Radius of the minimal enclosing ball.
.b [1x1] Squared norm of the center equal to Alpha'*K*Alpha.
.options [struct] Copy of used options.
.stat [struct] Statistics about optimization:
.access [1x1] Number of requested columns of matrix H.
.t [1x1] Number of iterations.
.UB [1x1] Upper bound on the optimal value of criterion.
.LB [1x1] Lower bound on the optimal value of criterion.
.LB_History [1x(t+1)] LB with respect to iteration.
.UB_History [1x(t+1)] UB with respect to iteration.
.NA [1x1] Number of non-zero entries in solution.
Example:
data = load('riply_trn');
options = struct('ker','rbf','arg',1);
model = minball(data.X,options);
[Ax,Ay] = meshgrid(linspace(-5,5,100),linspace(-5,5,100));
dist = kdist([Ax(:)';Ay(:)'],model);
figure; hold on;
ppatterns(data.X); ppatterns(model.sv.X,'ro',12);
contour( Ax, Ay, reshape(dist,100,100),[model.r model.r]);
See also
KDIST.
About: Statistical Pattern Recognition Toolbox
(C) 1999-2005, Written by Vojtech Franc and Vaclav Hlavac
Czech Technical University Prague
Faculty of Electrical Engineering
Center for Machine Perception
Modifications:
24-july-2008, VF: fixed problem with computing r; pointed out by Daewon Lee (MPI, Tuebingen)
09-nov-2006, VF, added C; requested by Hsiung, Chang
24-jan-2005, VF, Fast GMNP solver used.
25-aug-2004, VF, added model.fun = 'kdist' and .diag_add changed to .mu
16-may-2004, VF
15-jun-2002, VF