I want to know how to multiply array elements one by one.

Hello, I have some problems with making matlab code.

If I have 2x2 matrix. I want to calculate (1,1)x(1,1), (1,1)x(1,2) (1,1)x(2,1), (1,1)x(2,2)

(1,2)x(1,2), (1,2)x(2,1), (1,2)x(2,2) -> (1,2)x(1,1) is already exists in the first row.

(2,1)x(2,1), (2,1)x(2,2) -> (2,1)x(1,1), (2,1)x(1,2) are already existed in the previous rows.

(2,2) values.

(1,1) is the element of matrix value. for example) if matrix [1,2,3;4,5,6;7,8,9], then (1,1) means 1.

So, what I want to say is (1,1)x(1,2) = 1x2=2.

I want to expand this to m x m matrix.

how I make the code or which function should I use?

Until now I have used just ' for '.

I made the code with 4 parameter (ex) i,j,k,l)

However, this operation has duplicate values, and as the matrix becomes large, the operation speed becomes significantly longer.

plz help me....

[KSSV]

(1,1)x(1,1)

x(1,1) is the element from first row and first column. What is (1,1) before to x(1,1)?

[용준 권]

(1,1) is the element of matrix value. for example) if matrix [1,2,3;4,5,6;7,8,9], then (1,1) means 1.

So, what I want to say is (1,1)x(1,2) = 1x2=2.

[Torsten]

Can you show the expected result for the matrix

[1,2,3;4,5,6;7,8,9]

and the way you want to save this result ?

[용준 권]

Calculating as I intended gives a total of 45 results, so I'll collapse the matrix to [1,2;3,4].

Then, (1,1)x(1,1) = 1x1 = 1, (1,1)x(1,2) =1x2 = 2, (1,1)x(2,1) = 1x3 = 3, (1,1)x(2,2) = 1x4=4

(1,2)x(1,2) = 2x2 = 4, (1,2)x(2,1) = 2x3 = 6, (1,2)x(2,2) = 2x4 = 8 .

(2,1)x(2,1) = 3x3 =9 , (2,1)x(2,2) = 3x4 = 12

(2,2)x(2,2) = 4x4 = 16.

And I will save this result to the n x 2 matrix. In the above case, n=10.

If I use 3x3 matrix then, n=45.

The first column is the distance. That means, if I calculate (1,2)x(2,2), then the distance is the sqrt((2-1)^2+(2-2)^2). if i calculate (1,2)x(3,4), then the distance is the sqrt(3-1)^2+(4-2)^2).

and the second column is the calculated value. That means if I calculate (1,2)x(2,2), then the value is 12.

[Torsten]

That means if I calculate (1,2)x(2,2), then the value is 12.

I thought the value was 8.

[용준 권]

1st column is for the distance between two matrix elements.

2nd column is for the product of two elements.

if I calculate (1,2)x(2,2), then the distance is the sqrt((2-1)^2+(2-2)^2).

the second column is the calculated value. That means if I calculate (1,2)x(2,2), then the value is 12.

[용준 권]

oh sorry! you are right. I missed. (1,2)x(2,2) is 2x4 = 8.

Answer 1

[Arif Hoq]

A=[1 2; 3 4];
B1=A(1,1)*A(:);
B2=A(1,2)*A(:);
B3=A(2,1)*A(:);
B4=A(2,2)*A(:);
matrix=[B1 B2 B3 B4];
out=reshape(matrix,1,[]);
out2=unique(out)

out2 = 1×9

1 2 3 4 6 8 9 12 16

And I will save this result to the n x 2 matrix. In the above case, n=10.

no, its 9 element row vector. so you can not reshaped into n X 2 arrray.

[Arif Hoq]

A=[1 2; 3 4];
C=cell(size(A,2),1);
for j=1:size(A,2)
    for k=1:size(A,2)    
   C{j,k}=A(j,k)*A(:);
end
end
matrix=[C{:}];
out=reshape(matrix,1,[]);
out2=unique(out)

out2 = 1×9

1 2 3 4 6 8 9 12 16

[Torsten]

Why the "unique(out)" ?

The OP only wanted to point out that some elements are calculated several times and how this could be avoided for the sake of efficiency.

[용준 권]

Thanks for your reply.

In this case, I will not use the unique function. Ironically, in the final results(In your code, it is the 'out' variable.), duplicate values are important for me.

The duplicate values ​​I said in the question mean things like (1,2)x(2,1) and (2,1)x(1,2).

And I will use the more big matrix, for example, minimum 100 x 100 to maximum 10000x10000?.

But your answer is very helpful for me.

thank you!

[용준 권]

B2's A(1,2)*A(2,1) and B3's A(2,1)*A(1,2) are duplicate values. I don't need this operation.

But, A(1,1)xA(2,2) = 1x4=4, A(1,2)xA(1,2) = 2x2 = 4 is different from the above.

The redundancy of the multiplication is unnecessary, but the redundancy of the result is important.

[용준 권]

So, what i want to say is I want to avoid redundancy in multiplication.