How to Copy Upper diagonal elements of matrix A into a new matrix.

A= 1 2 3 4; 2 1 3 4; 1 1 1 2; 1 0 0 1 Then how to copy the upper diagonal elements into a new Matrix using for loops etc.

Answer 1

[Jan]

A = [1 2 3 4; 2 1 3 4; 1 1 1 2; 1 0 0 1];
B = triu(A)

B = 4×4

1 2 3 4 0 1 3 4 0 0 1 2 0 0 0 1

Answer 2

[Awais Saeed]

A= [1 2 3 4; 2 1 3 4; 1 1 1 2; 1 0 0 1]

A = 4×4

1 2 3 4 2 1 3 4 1 1 1 2 1 0 0 1

M = zeros(size(A));
for row = 1:1:size(A,1)
	for col = row:1:size(A,2)
		M(row,col) = A(row,col);
	end
end
disp(M)

     1     2     3     4
     0     1     3     4
     0     0     1     2
     0     0     0     1

[Usman Mussadiq]

for i=1:n

for j=1:n

if i~=j && i<j

index1(1,ind) = i;

index2(1,ind) = j;

ind=ind+1;

for r=1:p(3)

temp(k,r) = A(i,j,r);

end

k=k+1;

end

end

end

please explain it to me how it is working.

[Usman Mussadiq]

Sorry i am not so expert in matlab and wasting your precious time, but i need your help to understand the same algo.

[Awais Saeed]

I answered exactly as per your question "how to copy the upper diagonal elements into a new Matrix using for loops".

Why do you care how your developer is doing things. If you think he is making a mistake or he needs help in doing what you asked in your question then just simply show him the proposed answer. If he does not like doing it in a For Loop then use triu(A) as @Jan have mentioned.

[Usman Mussadiq]

Thank You @Awais Saeed

Answer 3

[KSSV]

You need to proceed like this:

for i = 1:m
    for j = 1:n
        if i <= j

        end
    end
end

[Usman Mussadiq]

for i=1:n

for j=1:n

if i~=j && i<j

index1(1,ind) = i;

index2(1,ind) = j;

ind=ind+1;

for r=1:p(3)

temp(k,r) = A(i,j,r);

end

k=k+1;

end

end

end

will you explain it to me?? how it is working, please

[Usman Mussadiq]

please suppose 2 matrix like A and temp are considered, what is role of r here and how indices are matched,

[Jan]

@Usman Mussadiq: Your A has 3 dimensions, so it is not a "matrix". Matrices are 2D by definition.

In your code ind, k and p are undefined. It is not meaningful to explain code, if we have to guess, what it should do. This code does not match the question, because it is not a copy of a triangular matrix.

In

if i~=j && i<j

The i~=j is not useful: If i < j, the case i==j is excluded already.

[Usman Mussadiq]

@Jan

A(:,:,j)= [1,2,8,1;1,1,5,1;8,5,1,7;7,6,7,1];
n = size(A);
ind=1;
k=1;
p=size(A);

[Usman Mussadiq]

@Jan it is mentioned by the algo developer that he is copying the upper diagonal elements into temp, but in my understanding this code is generating a full matrix from the upper triangular elements only. Please guide me.

[Jan]

I do not know what "copy into temp" means.

Maybe you want to get a vector with only the elements of the upper triangular matrix?

mask = (1:4) > (1:4).';   % Or >= ?
temp = A(mask)