Why is str2num not recommended when it is faster in certain circumstances?

I have a cell array of millions of strings representing dates with the format "yyyyMMddHHmmss"
I need to convert these to datetimes. After many attempts of various kinds I think I have found an optimal solution.
However, my solution requires that I use str2num instead of str2double and results in nearly 100x increase in speed. This is depite the fact that MATLAB recommends using str2double for "faster performance" and specifically discourages str2num.
In particular, str2double cannot convert a char array and results in Inf, while str2num converts the char array without issue.
Below is an example script.

(P.S. not directly related to this question, but if there is a faster way to convert cell arrays of strings to datetimes, let me know!)

%Make example input data
t1 = datetime(2000,1,1,0,0,0);
t2 = datetime("now");
t = string(datestr(t1:days(1):t2,’yyyymmddHHMMss’));

t_cell = cellstr(t); %<— This is the "cell array" example data

%Option 1: datetime cell array of strings
% —> Very slow (~0.75 s)
tic
tcheck1 = datetime(t_cell,’InputFormat’,’yyyyMMddHHmmss’);
toc

%Option 2: str2double
% —> DOES NOT WORK (results in Inf)
tic
da = char(t_cell);
year1 = str2double(da(:,1:4));
month1 = str2double(da(:,5:6));
day1 = str2double(da(:,7:8));
hour1 = str2double(da(:,9:10));
min1 = str2double(da(:,11:12));
sec1 = str2double(da(:,13:14));
tcheck2 = datetime(year1,month1,day1,hour1,min1,sec1);
toc

%Option 3: str2double with extra conversion from char to string
% —> About twice as fast as Option #1 (~0.4 s)
tic
da = char(t_cell);
year1 = str2double(string(da(:,1:4)));
month1 = str2double(string(da(:,5:6)));
day1 = str2double(string(da(:,7:8)));
hour1 = str2double(string(da(:,9:10)));
min1 = str2double(string(da(:,11:12)));
sec1 = str2double(string(da(:,13:14)));
tcheck3 = datetime(year1,month1,day1,hour1,min1,sec1);
toc

%Option 3: str2num
% —> About 100 times faster than Option #1 and #3 (~0.005 s)
tic
da = char(t_cell);
year1 = str2num(da(:,1:4));
month1 = str2num(da(:,5:6));
day1 = str2num(da(:,7:8));
hour1 = str2num(da(:,9:10));
min1 = str2num(da(:,11:12));
sec1 = str2num(da(:,13:14));
tcheck4 = datetime(year1,month1,day1,hour1,min1,sec1);
tocI have a cell array of millions of strings representing dates with the format "yyyyMMddHHmmss"
I need to convert these to datetimes. After many attempts of various kinds I think I have found an optimal solution.
However, my solution requires that I use str2num instead of str2double and results in nearly 100x increase in speed. This is depite the fact that MATLAB recommends using str2double for "faster performance" and specifically discourages str2num.
In particular, str2double cannot convert a char array and results in Inf, while str2num converts the char array without issue.
Below is an example script.

(P.S. not directly related to this question, but if there is a faster way to convert cell arrays of strings to datetimes, let me know!)

%Make example input data
t1 = datetime(2000,1,1,0,0,0);
t2 = datetime("now");
t = string(datestr(t1:days(1):t2,’yyyymmddHHMMss’));

t_cell = cellstr(t); %<— This is the "cell array" example data

%Option 1: datetime cell array of strings
% —> Very slow (~0.75 s)
tic
tcheck1 = datetime(t_cell,’InputFormat’,’yyyyMMddHHmmss’);
toc

%Option 3: str2num
% —> About 100 times faster than Option #1 and #3 (~0.005 s)
tic
da = char(t_cell);
year1 = str2num(da(:,1:4));
month1 = str2num(da(:,5:6));
day1 = str2num(da(:,7:8));
hour1 = str2num(da(:,9:10));
min1 = str2num(da(:,11:12));
sec1 = str2num(da(:,13:14));
tcheck4 = datetime(year1,month1,day1,hour1,min1,sec1);
toc I have a cell array of millions of strings representing dates with the format "yyyyMMddHHmmss"
I need to convert these to datetimes. After many attempts of various kinds I think I have found an optimal solution.
However, my solution requires that I use str2num instead of str2double and results in nearly 100x increase in speed. This is depite the fact that MATLAB recommends using str2double for "faster performance" and specifically discourages str2num.
In particular, str2double cannot convert a char array and results in Inf, while str2num converts the char array without issue.
Below is an example script.

(P.S. not directly related to this question, but if there is a faster way to convert cell arrays of strings to datetimes, let me know!)

%Make example input data
t1 = datetime(2000,1,1,0,0,0);
t2 = datetime("now");
t = string(datestr(t1:days(1):t2,’yyyymmddHHMMss’));

t_cell = cellstr(t); %<— This is the "cell array" example data

%Option 1: datetime cell array of strings
% —> Very slow (~0.75 s)
tic
tcheck1 = datetime(t_cell,’InputFormat’,’yyyyMMddHHmmss’);
toc

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