David - yes the problem is with your condtion. Note that size will return an array where each element is the size of the dimension. Trying to compare this to 4 2 will result in an Unexpected MATLAB expression error (at least it does for me) so you need to think of an alternative way to do this check. From size, you can get the number of rows and the number of columns by supplying the appropriate dimension input.
numberOfRows = size(n,1);
numberOfColumns = size(n,2);
Now that you know the size of each dimension, you can then do the appropriate comparison
if size(n,1) == 4 && size(n,2) == 2
% congrats...
end
One further check that you may want to add is to ensure that the number of dimensions is two (since a 4x2x3 matrix will pass the above condition). See ndims for details.
