cellstr(num2str('Best_pos(1:4)'))'
'Best_pos(1:4)' is a character vector. num2str() applied to a character vector gives the character vector. cellstr() applied to the character vector wraps it in a cell array, giving you a 1 x 1 cell array.
You mention that ParsListMain is 1 x 4, but you do not indicate what data type it is. If it were numeric then in context of the [] with the 1 x 1 cell array, then the numeric content would be wrapped in a cell and you would get a 2 x 1 cell array. If, though, ParsListMain is a 1 x 4 cell array then you would be doing vertcat between a 1 x 4 cell and a 1 x 1 cell, and that would be an error.
If Best_pos happens to be a numeric row vector then in
Pars = reshape([ParsListMain; cellstr(num2str(Best_pos(1:4)))'],1,[]);
the indexing Best_pos(1:4) of the (assumed) row vector would give you a 1 x 4 numeric vector, and num2str() of a numeric vector gives you a 1 x whatever character vector, and you would be back to the same problem as before.
If Best_post happens to be any other shape other than row vector (in particular if it happens to be a column vector) then Best_pos(1:4) would give you a 4 x 1 numeric vector, and num2str() of that would give you a 4 x whatever character array, cellstr() of which would give you a 4 x 1 cell array. Which you then transpose to 1 x 4. vertical concatenation of that with a 1 x 4 cell array could work fine.
