Where am I wrong in the following?

79 Views Asked by At

We have matrix $D$ as follows $$\begin{bmatrix} d_{1,1} & d_{2,1} & d_{3,1}\\ d_{1,2} & d_{2,2} & d_{3,2}\\ d_{1,3} & d_{2,3} & d_{3,3} \end{bmatrix}.$$ For this matrix a research paper shows that the elements of the matrix follow following properties

  1. Every entry is non-negative.
  2. For every $1\leq j\leq 3$, $$\sum_{\tilde{k}=1}^3 d_{j,\tilde{k}}+\sum_{\tilde{j}=1,\tilde{j}\neq j}^3\max_k\{ d_{\tilde{j}k}\}\leq 1 \tag{1}.$$

After two pages the same research paper writes the second property as follows: $$\sum_{\tilde{k}}^{3}d_{j,\tilde{k}}+\max_k\left\{ \sum_{\tilde{j}=1,\tilde{j}\neq j}^3 d_{\tilde{j}k} \right\} \leq 1 \qquad \forall\ j\in\{1,2,3\}. \tag{2}$$

I tried to verify that left hand sides of (1) and (2) produce same results for $j = 1$, but (1) produces $$\sum_{\tilde{k}=1}^3 d_{1,k}+\max\{d_{2,1},d_{2,2},d_{2,3}\}+\max\{d_{3,1},d_{3,2},d_{3,3}\}$$ while the left hand side of (2) produces $$\sum_{\tilde{k}=1}^3 d_{1,k}+\max\{d_{2,1}+d_{3,1},d_{2,2}+d_{3,2},d_{2,3}+d_{3,3}\}$$ which I think are not same. For example, consider the following matrix $$D=\frac{1}{11}\begin{bmatrix} 1 & 3 & 2\\ 2 & 1 & 3\\ 3 & 2 & 1 \end{bmatrix}.$$ For this matrix the (1) inequality is invalid while the (2) inequality is valid. Am I wrong somewhere or the left hand sides of (1) and (2) are not equal to each other. Any help in this regard will be much appreciated. Thanks in advance.

1

There are 1 best solutions below

0
On BEST ANSWER

The second inequality is implied by the first.

This is because for each fixed $j$ ($1 \leq j \leq 3$), and every $\tilde{j},k$ ($1 \leq \tilde{j}, k \leq 3$) with $\tilde{j} \neq j$, we have $$ \begin{alignat}{10} & & d_{\tilde{j}k} &\leq \max_{1 \leq k \leq 3}\{ d_{\tilde{j}k} \}\\ \implies & & \sum_{\tilde{j} = 1, \tilde{j} \neq j}^3 d_{\tilde{j}k} &\leq \sum_{\tilde{j} = 1, \tilde{j} \neq j}^3 \max_{1\leq k \leq 3}\{d_{\tilde{j}k}\} \\ \implies & & \max_{1 \leq k \leq 3} \left \{\sum_{\tilde{j} = 1, \tilde{j} \neq j}^3 d_{\tilde{j}k} \right\} &\leq \sum_{\tilde{j} = 1, \tilde{j} \neq j}^3 \max_{1\leq k \leq 3}\{d_{\tilde{j}k}\} \end{alignat} $$


The first inequality is not implied by the second, as you have shown with the counterexample.