You can't put multiple numbers into one element of a numeric array.
x = 1:10;
x(5) = ... % assigning to one element of x
[99 4]; % and trying to store two elements into it won't fit
You could use a cell array, or you could assign to a segment of the array large enough to fit the data you're trying to store in it.
C = cell(1, 10);
C{5} = ... % Note I'm using curly braces to assign to the contents of the fifth cell
[99 4]; % rather than assigning to the fifth cell itself.
% or
y = zeros(2);
y(1, :) = ... % Referring to all two columns in the first row of y
[99, 4]; % This has one row and two columns, the same size as the target of the assignment
