How to skip parameters in a function call

Hello,

i'd like to make a function that can be called even if only a part of its input parameters are defined in the call.

I.e.:

Function definition is something along this lines:

function [ret] = fun(a, b, c, d, e)

if ~exist('a','var')

% parameter a does not exist, so default it to something

a = 0;

end

if ~exist('b','var')

...

ret = [a,b,c,d,e];

return;

The function call should work something like this:

test_call_1 = fun(a=1,b=2,d=3,e=4); (here parameter c is not specified)

test_call_2 = fun(e=4); (here only parameter e is specified)

My function is already able to initialize any missing parameters with default values. I know about using "~" to specify that a parameter is skipped. However, this only works for defining the function, not when calling it (as is required here).

Any help is highly appriciated :)

Answer 1

[Star Strider]

See the documentation section on Support Variable Number of Inputs for a demonstration of how to do that.

[Dominik Hildebrand]

Thank you for your quick answer!

However, I have already come across this section and I believe it does not solve my problem:

The described solution is for a function with variable and/or repeating arguments, like:

f_var(a_1,b_1, ... , a_n, b_n) with calls like f_var(1,2, ..., n)

However, in my case we have a function that uses a fixed amount of inputs where some of the inputs may be skipped. Perhaps this function is a better example:

f_fix[ret](a, b, c, d):

ret = [a, b, c, d];

And calls are like:

f_fix(a) which returns [a, 0, 0, 0]

f_fix(a, d) which returns [a, 0, 0, d]

f_fix(b, c) which returns [0, b, c, 0]

However, calls like f_fix(a,b,c,d,e) would result in an error since this function takes at max 4 inputs.

[Star Strider]

I’m lost.

As a general rule, the way MATLAB handles missing inputs is to substitute the empty array [] for them in the function call.

So to omit ‘b’:

out = fcn(a,[],c);

although ‘b’ would have to have a default value assigned in the function once it is detectred as missing.

Try that.

EDIT — (7 Jul 2021 at 15:18)

Added this example —

out = fcn(1,[],3)

out = 1×3 cell array
    {[1]}    {[0]}    {[3]}

function out = fcn(varargin)
a = varargin(1);
b = varargin(2);
c = varargin(3);
if isempty(a{:})
    a = 0;
end
if isempty(b{:})
    b = 0;
end
if isempty(c{:})
    c = 0;
end
out = [a,b,c];
end

.

[Dominik Hildebrand]

Thank you again for your help :D

I feel your solution is as good as it gets, but for sake of completness ill include my final "draft" as well:

function [ ret ] = fun(a, b, c, d)

default_param = 0;

if ~exist('a','var') || isempty(a)

a = default_param;

end

if ~exist('b','var') || isempty(b)

b = default_param;

end

if ~exist('x','var') || isempty(x)

c = default_param;

end

if ~exist('c','var') || isempty(c)

d = default_param;

end

ret = [a,b,c,d];

return;

[Star Strider]

As always, my pleasure!

Thank you!

Noted.

.