On rank range of interval matrices

An interval matrix is a matrix whose entries are intervals in the set of real numbers. Let $p , q$ be nonzero natural numbers and let $\mu =( [m_{i,j}, M_{i,j}])_{i,j}$ be a $p \times q$ interval matrix; given a $p \times q$ matrix $A$ with entries in the set of real numbers, we say that $A \in \mu$ if $a_{i,j} \in [m_{i,j}, M_{i,j}]$ for any $i,j$. We establish a criterion to say if an interval matrix contains a matrix of rank $1$. Moreover we determine the maximum rank of the matrices contained in a given interval matrix. Finally, for any interval matrix $\mu$ with no more than $3$ columns, we describe a way to find the range of the ranks of the matrices contained in $\mu$.Comment: corrected Section