For matrix A you cannot do: A.^2(:)

I have a matrix A=[1 2;3 4]. I want to sum the squares of the elements in the matrix. So I tried

sum(A.^2(:))

I cannot do this. The problem is A.^2(:). How do I solve this? Parenthesis around A.^2 does not help.

A workaround is

sum(reshape(A.^2,[],1))

Related to this is for example:

1+A(:)

This is OK. But this is not:

A+1(:)

Parenthesis around A+1 does not work.

[Paul]

A=[1 2;3 4];
1 + A(:)

ans = 4×1

2 4 3 5

% A + 1(:) not sure what this is expected to do?
% maybe
A + 1

ans = 2×2

2 3 4 5

% or
A(:) + 1

ans = 4×1

2 4 3 5

[Eric]

The same as 1+A(:).

Answer 1

[Matt J]

You cannot apply ()-indexing to mathematical expressions, function calls, or literal constants, only to variables. So, in your case, you would do,

sum(A(:).^2)

Note that the result of other indexing expressions are considered variables for this purpose, so these are okay:

s.a={[5,1]}; s.b=[10,3,2];

s.a{1}(:)

ans = 2×1

5 1

s.b(:)

ans = 3×1

10 3 2

Answer 2

[Catalytic]

A=[1 2;3 4];

sum(A(:).^2)

ans = 30

vecnorm(A(:))^2

ans = 30

norm(A,'fro')^2

ans = 30