How to use for loop compare all values in a 2x2 matrix?

Hi.

I'm a beginner and I'm just starting to learn Matlab so I'm not very familiar with the code syntax right now. But I'm working on the following problem.

A = [1, 2; 4, 6]

How do you use for loop to compare all the values in A to see which ones are greater than 3 and have those added together to make D?

Thanks.

Answer 1

[KSSV]

It is your home work...so you have to do it yourself. Follow the below hints.

1. You can get the dimensions/ size of a matrix using size.
2. You can comapre the elements using inequalitties >, <. >=, <=.
3. Also you can use logical indices striaght away with out loop.
4. To add you have to use +.

[Yuan Yuan Lin]

So far, I have:

A = [1 2; 4 6];

for (i = 1:4)

if(A[i] > 3)

D = D + A[i]

end

But it doesn't seem to be working.

[KSSV]

A = [1 2; 4 6];
[m,n] = size(A) ; 
D = 0 ; 
for i = 1:m   % loop for row 
    for j = 1:n   % loop for column 
         if(A(i,j) > 3)   % should use A() not A[]
            D = D + A(i,j) ;
         end
    end    
end

Withput loop

idx = A(:) > 3 ;
D = sum(A(idx)) ; 

[Yuan Yuan Lin]

What does A(:) mean? I understand how sum() works. But what's A(idx)?

[KSSV]

You can try what A(:) prints, in command window instead of asking a question. This will help ypu to understand yourself. Anything, you have a doubts just type in command window and see it. You can get yourself.

A(:) this will make a matrix into a single column vector.

idx gives logical indices whose values are >3.

[Yuan Yuan Lin]

Okay. I'll try it on my own. Thank you.