Iris recognition using filters?
Given a matrix A that consists of zeros and ones only (which you should have after step 4 of your algorithm, you could implement step 5 via the following:

% find column with the maximum number of ones. sum down the rows of the
% matrix and find the column with the largest sum
[ry,xo] = max(sum(A));
% find the corresponding row; do the same thing except sum across the
% matrix's columns
[rx,yo] = max(sum(A,2));
% the values "rx" and "ry" above contain the sums of the row and column
% (respectively) that have the maximum number of ones. divide them by
% 2 according to your algorithm in step 5
rx = rx / 2;
ry = ry / 2;


After the above (which is untested), then xo, yo, rx, and ry should be populated with the values that your algorithm indicated.