# How many row and column spaces do I need to make two matrices zero?(Fixed)

Here is problem.

Let's say we have two $m \times n$ matrices $A$ and $B$.

I want to find the minimum $m+n$ such that

there exists $v_1,\cdots,v_m \in \mathbb{R}^m$ and $u_1,\cdots,u_n \in \mathbb{R}^n$ and $a_1,\cdots,a_m \in \mathbb{R}^n$ and $a_1',\cdots,a_m' \in \mathbb{R}^n$ and $b_1,\cdots,b_n \in \mathbb{R}^m$ and $b_1',\cdots,b_n' \in \mathbb{R}^m$ satisfying

$A+ \sum_i v_ia_i^T + \sum_j b_iu_i^T = 0$

and

$B+ \sum_i v_ia_i'^T + \sum_j b_i'u_i^T= 0$.

The answer has to greater or equal to $max_{\lambda_1,\lambda_2} rank(\lambda_1 A + \lambda_2 B)$. Is this bound tight?

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$\sum_i a_iv_i$ is a vector, while $A$ is a matrix; something seems to be missing in your formulation. –  Suvrit Nov 11 '10 at 18:06
The bug is fixed. –  Seyong Nov 11 '10 at 18:16
But the indexing is not fixed. Gerhard "Ask Me About System Design" Paseman, 2010.11.11 –  Gerhard Paseman Nov 11 '10 at 18:26