Matlab Function Block Array Size

Hello

I have a MATLAB function block in Simulink, with and output that changes its size. I know that the size has to be defined in order for it to work, but this cant be done before the block actually runs. What I do know, is that the output size can be from a 2x2 matrix, not bigger than 1000x3 (actually a 1000x2 :) ) matrix. I read that there is a way to define "bounds" for the size of the output, so I don't have to exactly define the matrix size of the output, and all the possible sizes inside the bounds will be okay.

How do I do this?

Thanks in advance