l2q2d.m

this a SVM toolbox,it is very useful for someone who just learn SVM.In order to be undestood easily,

function [A,B,C]=l2q2d(alpha,theta)
% L2Q2D transforms 5D hyperplane to 2D quadratic function.
%  [A,B,C]=ltoq2d(alpha,theta)
%
% L2Q2D transforms coefficients of hyperplane in 5D space
%   to coefficients of quadratic surface in 2D space.
%
%     5D: alpha'*y=theta   ==>  2D: x'Ax + B'x + C = 0
%
%   This problem is related to quadratic non-linear mapping
%   (see help qtransf).
%
% Input:
%   alpha [5x1], theta [1x1] coefficients of hyperplane.
%
% Output:
%   A [2x2], B [2x1], C [1x1] coefficients of quadratic surface.
%
%
% See also QTRANSF, QUADEMO.
%

% Statistical Pattern Recognition Toolbox, Vojtech Franc, Vaclav Hlavac
% (c) Czech Technical University Prague, http://cmp.felk.cvut.cz
% Written Vojtech Franc (diploma thesis) 19.11.1999
% Modifications
% 24. 6.00 V. Hlavac, comments polished.

A(1,1)=alpha(3);
A(1,2)=alpha(4)/2;
A(2,1)=alpha(4)/2;
A(2,2)=alpha(5);
B(1)=alpha(1);
B(2)=alpha(2);
C=-theta;