It is not certain what you want to do. We don’t know what scalars or arrays you’re concatenating, so I would create ‘polyX’ as a cell array, since cell arrays are much more tolerant of changing dimensions than matrices:
polyX{i} = horzcat(X2(i),X1(i+1),V(i+1));
Note the curly braces ‘{}’ denoting that ‘polyX’ is now a cell array. See the documentation on Cell Arrays for details.
