What value or values do you want to be stored in Ma before that line of code executes? Take a look at the list of functions in the "Create and Combine Arrays" section and the "Creating, Concatenating, and Expanding Matrices" Topic on this documentation page for some functions that may be useful in defining your Ma vector.

How about putting a NaN in it? Data(n,1)= NaN;

The first method is the slowest because even when the matrix is preallocated, its size changes within the loop, what renders the first preallocation useless. The system has to look for increasing room for a growing matrix. The third method is slower than the second because it preallocates the matrix but with no specific size, the problem is similar to the first method but faster because the matrix is not overwritten. The second method gives more freedom to the system to locate the matrix.

for i = 1:numel(Result) [r, c]= size(Result{i}); assert(c == 1, 'Number of columns must be 1.') if r < 5, Result{i}{5,1} = []; end end