How to test function inputs for vector/scalar?

I am coding for an assignment in which I have a function. The function has 3 inputs. The first two inputs need to be combined in a single vector for their input, and the other input is a scalar. The first thing my function needs to do is test if the inputs are in the correct format (the first 2 inputs being in a single vector and the third input being a scalar). I would prefer to use an IF statement to do this test, so how does one test for wether the inputs are the correct format?

For a bit of background, here is my function definition

function [wire_length,spring_mass] = spring_length_mass([inner_diameter outer_diameter],number_coils)

it would then go into the IF statement to test for proper input format.

Answer 1

[Voss]

You cannot concatenate things in a function definition like this:

function [wire_length,spring_mass] = spring_length_mass([inner_diameter outer_diameter],number_coils)
%                                                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ can't do this here

Instead make those two variables a single input (say, diameters) in the function definition and then separate them (if you must) after you check that diameters has two elements:

function [wire_length,spring_mass] = spring_length_mass(diameters,number_coils)

if numel(diameters) == 2
    inner_diameter = diameters(1);
    outer_diameter = diameters(2);
else
    error('Incorrect number of diameters given.')
end

if ~isscalar(number_coils)
    error('number_coils must be a scalar.')
end

% ... calculation of wire_length and spring_mass ...

end

Note that this allows diameters to be a 3D (or higher dimensional) array, which is not a vector, as long as it has 2 elements, such as diameters=rand(1,1,2). If you really want to constrain diameters to be a 1-by-2 vector or a 2-by-1 vector, you can use isvector.

You may also need/want to check that the correct number of inputs is given, for which you can use nargin.

https://www.mathworks.com/help/matlab/ref/isvector.html

https://www.mathworks.com/help/matlab/ref/isscalar.html

https://www.mathworks.com/help/matlab/ref/nargin.html