N=50;
n =N/2;
randn('state',6);
x1 = randn(2,n);
y1 = ones(1,n);
x2 = 5+randn(2,n);
y2 = -ones(1,n-1);
y2(1,n)=1;

figure;
plot(x1(1,:),x1(2,:),'b*',x2(1,1:n-1),x2(2,1:n-1),'k.',...
    x2(1,n),x2(2,n),'b*');
axis([-3 8 -3 8]);
hold on;

X1 = [x1,x2];
Y1 = [y1,y2]; 
X=X1';
y=Y1;
x=X;
C=50;
[g,z,a,k,d,m]=matlabsvm1(C,X,y,x)

a0=a';
for i=1:size(k,2)
    if a0(k(i))~=C
       plot(X(k(i),1),X(k(i),2),'s')
    elseif a0(k(i))==C
       plot(X(k(i),1),X(k(i),2),'ro') 
    end
end

pp=-3:0.1:8;
A=sum(a.*(y').*X(:,2));
B=sum(a.*(y').*(X*(X(k(1),:))'))-y(k(1))-sum(a.*(y').*X(:,1))*pp;
E=B+1;
F=B-1;
t1=B/A;
t2=E/A;
t3=F/A;
plot(pp,t1,'r',pp,t2,'--',pp,t3,'--')