- Non-negativity: Since each element $a_{ij}^2$ of the matrix $A$ is squared, $\sum_{i,j=1}^n a_{ij}^2 \geq 0$. Taking the square root of a non-negative number is also non-negative, hence $\|A\|_F = \sqrt{\sum_{i,j=1}^n a_{ij}^2} \geq 0$.
- Definiteness: If
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