Nargin, vargin, exist, what is the best way to implement optional arguments matlab

I have a function in matlab:

function output = myfunc(a,b,c,d,e)%a and b are mandetory%c d and e are optionalend

How would I handle inputs if a user gave an optional arg for e but not for c and d?

nargin just gives the number of arguments. would exist be the best way?

2

Best Answer

Just use nargin. It will tell you how many arguments are present. Use varargin only when you have a variable number of arguments, that is you have no limit in number of arguments, or you want to access the arguments in an indexing fashion. I assume this is not the case for you, so one solution might look like this.

function output = myfunc(a,b,c,d,e)%a and b are mandetory%c d and e are optionalif nargin < 3 || isempty(c)c = <default value for c>endif nargin < 4 || isempty(d)d = <default value for d>endif nargin < 5 || isempty(e)e = <default value for e>end<now do dome calculation using a to e><If a or b is accessed here, but not provded by the caller an error is generated by MATLAB>

If the user does not want to provide a value for c or d but provides e, he has to pass [], e.g. func(a,b,c,[],e), to omit d.

Alternatively you could use 

if nargin == 5<use a b c d and e>elseif nargin == 2<use a and b>else error('two or five arguments required');end

to check if all a arguments e are present. But this requires exactly 2 or 5 arguments.

You can to define c, d and e as optional and then assign values based on position. This requires empty inputs if they want e but not c. For example:

function output = myfunc( a, b, varargin )optionals = {0,0,0}; % placeholder for c d e with default valuesnumInputs = nargin - 2; % a and b are requiredinputVar = 1;while numInputs > 0if ~isempty(varargin{inputVar})optionals{inputVar} = varargin{inputVar};endinputVar = inputVar + 1;numInputs = numInputs - 1;endc = optionals{1};d = optionals{2};e = optionals{3};output = a + b + c + d + e;

This will just add everything together. There is alot of error checking that needs to happen with this. A better approach might be inputParser. This does paired inputs and checking. See Input Parser help

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