Guassian membership Function in NN

%inputs
% XOR input for x1 and x2
input = [0 0; 0 1; 1 0; 1 1];
% Desired output of XOR
output = [0;1;1;0];
% Initialize the bias
bias = [-1 -1 -1];
% Learning coefficient
coeff = 0.7;
% Number of learning iterations
iterations = 10000;
% Calculate weights randomly using seed.
rand('state',sum(100*clock));
weights = -1 +2.*rand(3,3);

%with back propogation
for i = 1:iterations
   out = zeros(4,1);
   numIn = length (input(:,1));
   for j = 1:numIn
      % Hidden layer
      H1 = bias(1,1)*weights(1,1)     
          + input(j,1)*weights(1,2)
          + input(j,2)*weights(1,3);

      % Send data through sigmoid function 1/1+e^-x
      % Note that sigma is a different m file
      % that I created to run this operation
      x2(1) = sigma(H1);
      H2 = bias(1,2)*weights(2,1)
           + input(j,1)*weights(2,2)
           + input(j,2)*weights(2,3);
      x2(2) = sigma(H2);

      % Output layer
      x3_1 = bias(1,3)*weights(3,1)
             + x2(1)*weights(3,2)
             + x2(2)*weights(3,3);
      out(j) = sigma(x3_1);
     
      % Adjust delta values of weights
      % For output layer:
      % delta(wi) = xi*delta,
      % delta = (1-actual output)*(desired output - actual output)
      delta3_1 = out(j)*(1-out(j))*(output(j)-out(j));
     
      % Propagate the delta backwards into hidden layers
      delta2_1 = x2(1)*(1-x2(1))*weights(3,2)*delta3_1;
      delta2_2 = x2(2)*(1-x2(2))*weights(3,3)*delta3_1;
     
      % Add weight changes to original weights
      % And use the new weights to repeat process.
      % delta weight = coeff*x*delta
      for k = 1:3
         if k == 1 % Bias cases
            weights(1,k) = weights(1,k) + coeff*bias(1,1)*delta2_1;
            weights(2,k) = weights(2,k) + coeff*bias(1,2)*delta2_2;
            weights(3,k) = weights(3,k) + coeff*bias(1,3)*delta3_1;
         else % When k=2 or 3 input cases to neurons
            weights(1,k) = weights(1,k) + coeff*input(j,1)*delta2_1;
            weights(2,k) = weights(2,k) + coeff*input(j,2)*delta2_2;
            weights(3,k) = weights(3,k) + coeff*x2(k-1)*delta3_1;
         end
      end
   end  
end

Activation Function in NN

% Illustration of various activation functions used in NN's
x = -10:0.1:10;
tmp = exp(-x);
y1 = 1./(1+tmp);
y2 = (1-tmp)./(1+tmp);
y3 = x;
subplot(231); plot(x, y1); grid on;
axis([min(x) max(x) -2 2]);
title('Logistic Function');
xlabel('(a)');
axis('square');
subplot(232); plot(x, y2); grid on;
axis([min(x) max(x) -2 2]);
title('Hyperbolic Tangent Function');
xlabel('(b)');
axis('square');
subplot(233); plot(x, y3); grid on;
axis([min(x) max(x) min(x) max(x)]);
title('Identity Function');
xlabel('(c)');
axis('square');