Use the link to understand more about the max function.
As to your query, here's what max(A, [ ], 2) does-
1) The max keyword tells that the maximum value has to be extracted from a vector/matrix
2) The first argument, 'A', is to pass the matrix A to the function.
3) The second argument is optional, and is used to pass a second matrix/vector to find out the maximum element from. That is, had the code been written as max(A, B), it would have returned the element from a corresponding dimension that was the largest among all elements from both A and B. Here, '[ ]' denotes that the maximum element is only to be returned from each dimension of the first argument only.
4) The third argument, '2', is used to tell the function that the maximum has to be found along the 2nd dimension (i.e, in this case, the maximum among all the columns in each row).
