plot(datetime(DATIMARmensili.Year(20:end,1),1,1),(DATIMARmensili.Month(20:end,1),1,1) DATIMARmensili.SMB_mpmm(20:end,1),'--co', 'MarkerEdgeColor','k','MarkerFaceColor','c', 'DisplayName','ECMWF');
^
At the marked place, you have just finished the second parameter (DATIMARmensili.Month(20:end,1),1,1) and then you have a space and then you have an expression. You do not have any operator between the () expression and the following DATIMARmensili expression.
In MATLAB, the cases in which it is permitted to have two expressions separated by a space, with no operator between them, are:
- You are at the first bracket nesting level within a [] list-building expression. For example, [1 a+2 3] is valid. In this case, the spaces are interpreted as-if you had a comma there, equivalent to [1, a+2, 3] in this example.
- You are at the first bracket nesting level within a {} cell-building expression. For example, {1 a+2 3} is valid. In this case, the spaces are interpreted as-if you had a comma there, equivalent to {1, a+2, 3} in this example.
... And that is it. Every other case in which you have two expressions in a row without an operator between them, is an error in MATLAB.
MATLAB has absolutely no implied multiplication. Not anywhere.
That said... your line is basically a mistake in nearly every component. I showed you a more correct line at https://www.mathworks.com/matlabcentral/answers/897572-how-to-plot-this-line#answer_766657
