issue in matrix multiplication

G=[1 1 1 1 1 0 0 0 1 0 0 0; 0 0 1 1 0 0 0 1 0 1 0 0; 1 1 1 0 1 0 0 1 0 0 1 0; 1 0 0 1 1 1 0 1 0 0 0 1];

m=[1 0 1 0]

how to multiply them??

Answer 1

[Youssef Khmou]

G is 4x12 and m is 1x4, then two possibilities :

 m*G
 G'*m'

You do not get binary result because of the multiplication cij=sum a_ik b_kj there is an addition. you can get binary results if the matrices have the same dimensions and you use Hadamard product :

m=m'
M=zeros(4,12);
for n=1:12
M(:,n)=m;
end
M.*G

Answer 2

[Wayne King]

   G=[1 1 1 1 1 0 0 0 1 0 0 0; 0 0 1 1 0 0 0 1 0 1 0 0; 1 1 1 0 1 0 0 1 0 0 1 0; 1 0 0 1 1 1 0 1 0 0 0 1];

m=[1 0 1 0];

out = m*G;

How else would you presume to multiply them?

[mary]

when i multiplied them using this way the result will be [ 2 2 3 2 2 0 0 2 1 1 1 0]

Answer 3

[Walter Roberson]

G is 12 x 4, and m is 1 x 4, so there is no direct way to multiply them. You can, however, use

G * m.'

to get 12 x 1, or you can use

m * G.'

to get 1 x 12

Possibly what you want is

G .* repmat(m.', 1, size(G,2))

[mary]

G is 4 by 12 if i multiply them directly the result is not binary ?? how come??

Answer 4

[sixwwwwww]

mary you can get desired output as follows:

G = [1 1 1 1 1 0 0 0 1 0 0 0; 0 0 1 1 0 0 0 1 0 1 0 0; 1 1 1 0 1 0 0 1 0 0 1 0; 1 0 0 1 1 1 0 1 0 0 0 1]';
m = [1 0 1 0];
idx = find(m);
result = zeros(1, size(G, 1));
for i = 1:size(G, 1)
    result(i) = sum(G(i, min(idx):max(idx)));
end
disp(result)

Do you need this?

[mary]

not this i need the result in binary .. just multiplying two matrices and the result would be binary

Answer 5

[Walter Roberson]

http://www.mathworks.com/matlabcentral/answers/35496-binary-matrix-multiplication