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matlaboperator-precedence

Why can't I employ operator precedence to write statement like $sum((A.^2)(:))$

I want to compute the L2 norm of a n-d matrix. I want to compute this in a single statement, without introducing temporal variables. But it seems I have to, because if I write it like this, it will complains unbalanced parenthesis,

sqrt(sum((A.^2)(:)))

So I have to introduce a temporal matrix B, to write like this

B = A.^2

sqrt(sum(B(:)))

Is there any technique I can use to avoid this? I also found that if a function returns a matrix, I also cannot write like this

(fun(A))(:)

My main concern is why the operator precedence does not work here.

Solution

  • There are several approaches for solving this in one line. One option is to use the reshape function, to reshape A into a vector, as follows:

    sqrt(sum(reshape(A,prod(size(A)),1).^2))

    Another option is to use Matlab's builtin function:

    sqrt(sum(builtin('_paren', A(:)).^2))