Why am I able to leave out the right-most arguments in a call to a function that doesn't need them under certain circumstances?

I am running R2018b - home use because I am working at home during the pandemic. Normally I would be using my licenced versions of MATLAB at NIST under the user email [e-mail]. I have received permission from MATLAB to do this.

I hope that the behavior illustrated below is a feature and not a bug that will be corrected in future versions, but can find no justification for it. If this turns out to be an important issue, I can take the time to trim the actual script down to a reasonable size to send to you so you can run it.

Illustrative portions of large script ...

rg = horzcat(r331, C1, Xg, Yg, Zg); % size(r331)= 3x3, the others are 3x1

R = SimRespMeas(rg, alpha); % SimRespMeas has 3 more arguments

...

kag = horzcat(k, [1;1;1], [1;0;0], [0;1;0], [0;0;1]);

Model = @(kag, alpha) SimRespMeas(kag, alpha); % SimRespMeas has 3 more arguments

[Kag, resnorm,residual,exitflag,output,lambda,jacobian] = lsqcurvefit (Model,kag,alpha,R,[],[],opts);

...

function R = SimRespMeas(rg, alpha, Xg, Yg, Zg)

if size(rg,2) == 4

Xq = Xg;

Yq = Yg;

Zq = Zg;

elseif size(rg,2) == 7

Xq = rg(:,5)/sqrt(sum(rg(:,5).^2)); % Normalized for RRF

Yq = rg(:,6)/sqrt(sum(rg(:,6).^2));

Zq = rg(:,7)/sqrt(sum(rg(:,7).^2));

else

disp('size(rg,2) must be 4 or 7');

crash

end

Both calls to SimRespMeas work without the arguments Xg, Yg, and Zg and give the same answer as when these arguments are explicitly included in the call to the function. I was going to add them to the function call after I generized the function this way, but forgot to do so and was very surprised when it ran without them. Is there somewhere in the MATLAB literature that says that this is allowed, or should I always include the redundant argument values when running the code even when they are not needed?

Thanks, Jon Geist

end % function SimRespMeas

[Stephen23]

The "Input Arguments" section on this page documents this behavior:

https://www.mathworks.com/help/matlab/matlab_prog/find-number-of-function-arguments.html#d122e44699

Answer 1

[Jon]

This is a feature. As long as you don't do a calculation within the function that needs the missing variables it will not throw an error. You can use the function nargin to detemine how many input arguments you have and branch accordingly

[Jon]

Here's a good reference on variable number of function argumentshttps://www.mathworks.com/help/matlab/input-and-output-arguments.html?s_tid=CRUX_lftnav