a example of BP Network to solve XOR problem

BPNetwork.m

w1=(rand(3,2)-0.5).*2+0.1;
w2=(rand(3,1)-0.5).*2+0.1;
ita=1;
alpha=1;

%x=[1 1;1 3;1 2;1 4];
%x=[ones(4,1).*(-1) x];

x=[0 0;1 1; 1 0; 0 1];
h=[0 0 0 0]';
tq=[1 1 -1 -1]';
flag=1;
total=1;
c=1;
while total~=0
    total=0;
    
   for i  = 1:4
       flag=1;
       while(flag>0)
           flag=0;
           I1=[-1,x(i,:)];
           O1=I1;
           I2=[-1,O1*w1];
           O2=tanh(I2*c);
           I3=O2*w2;
           O3=tanh(I3*c);
           h(i)=O3;
           abs(O3-tq(i))
           if(abs(O3-tq(i))>0.03) 
               flag=1;
               total=total+1;
               
               d1o=(O3-tq(i))*c*sech(c*I3).^2;
               d2=d1o*w2.*(sech(c*I2').^2)*c;
               d2=d2( 2:3 , 1 ) ;
               w2=alpha*w2-ita*O2'*d1o;
           
               w1=alpha*w1-ita*O1'*d2'
           end
           
          
       end
   end
   total
    
end
hold on;

for i = 1:4
    if(h(i)<0)
        plot(x(i,1),x(i,2),'rx');
        axis([-1 2 -1 2])
    else
        plot(x(i,1),x(i,2),'bo');
    end
end