Abstract: In this paper we describe strategies for recognizing and using hand drawn matrices in a pen math system. This includes a new technique to recognize common short-forms of writing matrices using ellipsis (. . . ). Ellipsis are commonly used in sketched matrices to illustrate the structure of a matrix without fully specifying the matrix. A second contribution of this paper is a new method to estimate the parameters of the hand drawn matrix, such as the number and position of the rows and columns. This is done using a modified clustering algorithm, allowing one to reduce the number of hard-coded constraints.