When you get() the Data from a uitable, the result is a cell array. If you want to convert the cell to a numeric matrix, use cell2mat(). For example,
X = cell2mat( get(handles.S, 'Data') );
One thing to watch out for is that it is not uncommon for the Data value of a uitable to be set to a cell array of strings, as using a cell array of strings allows you to control the exact format of the output display. If that has been done, if you are working with a cell array of strings that represent numbers, then you can use
X = str2double(get(handles.S, 'Data'));
with no cell2mat() needed. Note that any string not representable as a single number would be converted as NaN
