How to binary sum columns in a binary matrix

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Redfoxxie
Redfoxxie 2018-11-19
编辑： Redfoxxie 2018-11-19
Hello guys,
I hope you can help me, I'm currently studying the Hamming code in college, but it's only my second time using MatLab so i'm having some trouble answering this question:
"Calculate the minimum number of rows that you need to sum (XOR actually) on the Parity Test matrix so that you obtain a null vector, also indicate the row's index of the first set you found."
I made a rough translation of the question, but from my understading I need to sum(XOR) the values of each column, until I obtain a null vector.
In terms of coding this is what I have:
%2.6 - Parity Test Matrix
n = 255;
k = 247;
[H,G,n,k] = hammgen(8);
H=H'
And this gives me a huge binary matrix, let's assume that these few lines:
[1 0 0 0 0 0 0 0
0 1 0 0 0 0 0 0
0 0 1 0 0 0 0 0
...
1 1 1 0 0 0 0 0]
The sum of these 4 vectors should give me:
[0 0 0 0 0 0 0 0]
I have no idea how to this, can you guys please lend me a hand ? I hope the question is not confusing but i'm totally lost. I tried to use the sum() fuction but i got [128 128 128 128] or something in return.
Thanks in advance.

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James Tursa
James Tursa 2018-11-19
Just doing xor between succesive rows:
r = some row number
result = xor(H(r,:),H(r+1,:);
Can you wrap some code around this to get what you want?
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Redfoxxie
Redfoxxie 2018-11-19
编辑：Redfoxxie 2018-11-19
James, I tried the following:
n = 255;
k = 247;
[H,G,n,k] = hammgen(8);
H=H';
result = H(1,:)
for count=2:size(H,1)
result = xor(result,H(count,:));
if( all(result == 0))
disp('Im here')
break;
end
end
r = result
n_rows = count
This is the output:
result = 1 0 0 0 0 0 0 0
Im here
r = 0 0 0 0 0 0 0 0
count = 255
I'm guessing the code is running properly now, result has the proper vector for the first line of H, it enters the if condition when result has all 0 and the count was made up to 255 which is the total number of rows of the H matrix.
This is probably a characteristic of an Hamming Code, not sure though, but it seems the code is running as it should be, so thanks a lot James! If you notice any mistake on my part please let me know. Again, thanks.
James Tursa
James Tursa 2018-11-19
For readability, I would avoid using l for a variable name (looks too much like 1).

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