# Implementing a Neural Network in Matlab/Octave

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I am trying to solve the problem http://postimg.org/image/4bmfha8m7/

I am having trouble implementing the weight matrix for the 36 inputs.

I have a 3 neuron hidden layer.

I use the backpropagation algorithm to learn.

What I have tried so far is:

% Sigmoid Function Definition

function [result] = sigmoid(x)

result = 1.0 ./ (1.0 + exp(-x));

end

% Inputs

input = [1 1 0 1 1 1 0 1 0 1 0 1 1 1 0 0 0 0 0 0 0 1 1 1 0 0 1 1 1 0 0 1 1 1 0;

0 0 0 0 1 0 1 1 1 0 0 1 1 1 0 0 0 0 0 1 0 1 1 1 0 0 1 1 1 0 0 0 0 0 1;

0 0 0 0 0 0 1 1 1 1 0 1 1 1 1 0 1 1 1 1 0 1 1 1 1 0 1 1 1 1 0 0 0 0 0;

0 0 0 0 1 0 1 1 1 0 0 1 1 1 0 0 1 1 1 0 0 1 1 1 0 0 1 1 1 0 0 0 0 0 1];

% Desired outputs

output = [1;1;1;1];

% Initializing the bias (Bias or threshold are the same thing, essential for learning, to translate the curve)

% Also, the first column of the weight matrix is the weight of the bias values

bias = [-1 -1 -1 -1];

% Learning coefficient

coeff = 1.0;

% Number of learning iterations

iterations = 100;

disp('No. Of Learning Iterations = ');

disp(iterations);

% Initial weights

weights = ones(36,36);

% Main Algorithm Begins

for i = 1:iterations

out = zeros(4,1);

numIn = length (input(:,1));

for j = 1:numIn

% 1st neuron in the hidden layer

H1 = bias(1,1)*weights(1,1) + input(j,1)*weights(1,2) + input(j,2)*weights(1,3) + input(j,3)*weights(1,4)+ input(j,4)*weights(1,5) + input(j,5)*weights(1,6) + input(j,6)*weights(1,7)

+ input(j,7)*weights(1,8) + input(j,8)*weights(1,9) + input(j,9)*weights(1,10)+ input(j,10)*weights(1,11) + input(j,11)*weights(1,12) + input(j,12)*weights(1,13)

+ input(j,13)*weights(1,14) + input(j,14)*weights(1,15) + input(j,15)*weights(1,16)+ input(j,16)*weights(1,17) + input(j,17)*weights(1,18) + input(j,18)*weights(1,19)

+ input(j,19)*weights(1,20) + input(j,20)*weights(1,21) + input(j,21)*weights(1,22)+ input(j,22)*weights(1,23) + input(j,23)*weights(1,24) + input(j,24)*weights(1,25)

+ input(j,25)*weights(1,26) + input(j,26)*weights(1,27) + input(j,27)*weights(1,28)+ input(j,28)*weights(1,29) + input(j,29)*weights(1,30) + input(j,30)*weights(1,31)

+ input(j,31)*weights(1,32) + input(j,32)*weights(1,33) + input(j,33)*weights(1,34)+ input(j,34)*weights(1,35) + input(j,35)*weights(1,36)

x2(1) = sigmoid(H1);

% 2nd neuron in the hidden layer

H2 = bias(1,2)*weights(2,1) + input(j,1)*weights(2,2) + input(j,2)*weights(2,3) + input(j,3)*weights(2,4)+ input(j,4)*weights(2,5) + input(j,5)*weights(2,6) + input(j,6)*weights(2,7)

+ input(j,7)*weights(2,8) + input(j,8)*weights(2,9) + input(j,9)*weights(2,10)+ input(j,10)*weights(2,11) + input(j,11)*weights(2,12) + input(j,12)*weights(2,13)

+ input(j,13)*weights(2,14) + input(j,14)*weights(2,15) + input(j,15)*weights(2,16)+ input(j,16)*weights(2,17) + input(j,17)*weights(2,18) + input(j,18)*weights(2,19)

+ input(j,19)*weights(2,20) + input(j,20)*weights(2,21) + input(j,21)*weights(2,22)+ input(j,22)*weights(2,23) + input(j,23)*weights(2,24) + input(j,24)*weights(2,25)

+ input(j,25)*weights(2,26) + input(j,26)*weights(2,27) + input(j,27)*weights(2,28)+ input(j,28)*weights(2,29) + input(j,29)*weights(2,30) + input(j,30)*weights(2,31)

+ input(j,31)*weights(2,32) + input(j,32)*weights(2,33) + input(j,33)*weights(2,34)+ input(j,34)*weights(2,35) + input(j,35)*weights(2,36)

x2(2) = sigmoid(H2);

% 3rd neuron in the hidden layer

H3 =  bias(1,3)*weights(3,1) + input(j,1)*weights(3,2) + input(j,2)*weights(3,3) + input(j,3)*weights(3,4)+ input(j,4)*weights(3,5) + input(j,5)*weights(3,6) + input(j,6)*weights(3,7)

+ input(j,7)*weights(3,8) + input(j,8)*weights(3,9) + input(j,9)*weights(3,10)+ input(j,10)*weights(3,11) + input(j,11)*weights(3,12) + input(j,12)*weights(3,13)

+ input(j,13)*weights(3,14) + input(j,14)*weights(3,15) + input(j,15)*weights(3,16)+ input(j,16)*weights(3,17) + input(j,17)*weights(3,18) + input(j,18)*weights(3,19)

+ input(j,19)*weights(3,20) + input(j,20)*weights(3,21) + input(j,21)*weights(3,22)+ input(j,22)*weights(3,23) + input(j,23)*weights(3,24) + input(j,24)*weights(3,25)

+ input(j,25)*weights(3,26) + input(j,26)*weights(3,27) + input(j,27)*weights(3,28)+ input(j,28)*weights(3,29) + input(j,29)*weights(3,30) + input(j,30)*weights(3,31)

+ input(j,31)*weights(3,32) + input(j,32)*weights(3,33) + input(j,33)*weights(3,34)+ input(j,34)*weights(3,35) + input(j,35)*weights(3,36)

x2(3) = sigmoid(H3);

% Output layer

x3_1 = bias(1,4)*weights(4,1) + x2(1)*weights(4,2) + x2(2)*weights(4,3) + x2(3)*weights(4,4);

out(j) = sigmoid(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;

delta2_3 = x2(3)*(1-x2(3))*weights(3,4)*delta3_1;

% Add weight changes to original weights and then use the new weights.

% delta weight = coeff*x*delta

for k = 1:4

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)*delta2_3;

weights(4,k) = weights(4,k) + coeff*bias(1,4)*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*input(j,3)*delta2_3;

weights(4,k) = weights(4,k) + coeff*x2(k-1)*delta3_1;

end

end

end

end

disp('For the Input');

disp(input);

disp('Output Is');

disp(out);

disp('Test Case: For the Input');

input = [1 1 0 1 1 1 0 1 0 1 0 1 1 1 0 0 0 0 0 0 0 1 1 1 0 0 1 1 1 0 0 1 1 1 0];

by (105k points)

For me the problem is the labeling, I can't see where do you have the output

Output (1,1,1,1)? What do you mean? Perhaps I missed something but for me, there are two ways of labeling a multiclass classification one is with a label directly (0 for A, 1 for B, 3 for C...) and expanding it after or directly expanded like A=1,0,0,0 = [1,0,0,0;0,1,0,0,0,0,1,0,0,0,0,1]

You make operations are very easy to make mistakes, take a look at MatLab/octave matrix operations, it's very powerful and could simplify everything a lot.

If you wish to know more about Neural Network visit this Neural Network Tutorial.