using parse to deal with input arguments

Using R2008a, I created the following function:

function output = lm_applySAPO(Si, So, varargin)

p=inputparser;
p.addOptional('Si', 0.85, @(x) isscalar(x))
% parse(p, Si)

p.addOptional('So', 0.98, @(x) isscalar(x) && gt(x, p.Results.Si))
parse(p, Si, So)

output.Si = p.Results.Si;
output.So = p.Results.So;

end

Now when I call the function, I want to be able to call it with empty inputarguments for Si or So. As follows:

result = lm_applySAPO([] , 0.99)

This throws the following error message:

Error using lm_applySAPO (line 8)
Argument 'Si' failed validation @(x)isscalar(x).

My questions are as follows:

How can I use the inputparser object in combination with no values (using [ ]) for certain variables? I would really like to use [ ] when i can't provide a value for the input variable.

For the second addOptional I use p.Results.Si. This field in the struct seems already available without parsing the input (parse(p, Si) is commented). How is this possible?

Thanks,

[Martin]

Does this question have an answer yet?

I also would like to be able to call functions using inputparser with "empty" arguments, like in the call max([1 2;3 4],[],2).

Regards, Martin

Answer 1

[Adam]

Does it not work to just replace

isscalar(x)

with something like

validationFcn = @(x) isempty(x) || isscalar(x);

p.addOptional('Si', 0.85, @(x) validationFcn (x));

to deal with empty inputs?

[Martin]

Thanks,

I should clarify that I want the default value (provided in the call to addOptional) to be used if I input [], like for example the way interp1 works. Note that interp1 does not use the inputparser but rather a specific parsing function written for interp1 (only?).

So, is there a way to get the default value for "empty" ([]) argument using the inputparser tools, or do I need to write my own?

Regards, Martin

[Adam]

As far as I can see this is not possible with the builtin options for the inputparser though I may be wrong. I have looked at it numerous times, but have never actually used it as I don't generally have functions with varargin inputs.

You could do a post-parser check of attributes to assign defaults to any that are empty, but that is not especially neat I admit.

[Martin]

Yes, did a hack to get this functionality. I simply did a setdiff "between" all fieldnames in p.Results and p.UsingDefaults to get the fields having values supplied using varargin. Then I looped over those and reset the empty ones to the default values. Problem solved.

Thanks, Martin