How to return function arguments as a struct?

Hello people,

I am trying to create a function to help me solve some tedious math operations. I use a switch-case structure to compute different things depending on the input arguments, compute all the math and then return all the important information on a struct. Here is my code (I've deleted some case just do the example clearer):

function [varargout] = designSpec(varargin)
    switch varargin{1}
        % Case 1: ts and Mp are given
        case 1
            % Assign the variables
            ts = varargin{2}; % variables(1);
            Mp = varargin{3}/100; %variables(2)/100;
            % Validation of input arguments
            if nargin < 3
                error('Invalid number of inputs. Tolerance criteria for ts must be specified.');
            elseif varargin{4} == 2 % tolerance == 2
                ts_num = 4;
            elseif varargin{4} == 5
                ts_num = 3;
            end
            % Get the dominant poles
            damping = sqrt((log(Mp)^2)/((pi^2+(log(Mp)^2))));
            wn = ts_num/(damping*ts);
            sigma = -damping*wn; % real component
            wd = wn*sqrt(1-damping^2); % complex component
            poles = [sigma+wd*1i sigma-wd*1i];
            equation = poly(poles);
        % Case 2: tp and Mp are given
        case 2
            % Assign the variables
            tp = varargin{2};
            Mp = varargin{3}/100;
            % Get the dominant poles
            wd = pi/tp; % complex component
            tg_theta = -pi/log(Mp); % aux variable
            damping = sqrt(1/(1+tg_theta^2));
            wn = wd/sqrt(1-damping^2);
            sigma = -damping*wn; % real component
            poles = [sigma+wd*1i sigma-wd*1i];
            equation = poly(poles);
    end
    varargout{1} = equation;
    varargout{2} = poles;
    varargout{3} = wn;
    varargout{4} = damping;
end

The problem is that when I call the function it returns just the first argument of the function instead of returning a struct with all the variables in it. There is something that I'm missing on my code? Am I calling the function properly?

[Stephen23]

"There is something that I'm missing on my code?"

There is absolutely no "struct" involved anywhere in your code. You also don't use VARARGOUT in any way that makes use of its purpose (allowing a variable number of output arguments).

Your code is equivalent to simply defining the function signature as:

function [equation,poles,wn,damping] = designSpec(varargin)

Answer 1

[Paul]

Change the signature of the function to

function out = designSpec(varargin)

At the bottom of the function assign to the struct fields

out.equation = equation;
out.poles = poles;
out.wn = wn;
out.damping = damping;

[Diego Martinez]

Changing these two things solved the problem.

However I needed to change the output variable name to out instead of varargout, if not I get the error Variable output array "varargout" must be a cell array.

Some idea on why this is happening?

[Paul]

varargout is reserved for use typically when the number of outputs of the function aren't known until the function executes. It is a cell array, by definiton. But you wanted to return struct (with the same fields regardless of the specific inputs), so varargout wouldn't apply.

[Stephen23]

"Some idea on why this is happening?"

An output argument named VARARGOUT has a special meaning and behavior:

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

[Steven Lord]

varargout has a special meaning in MATLAB.

[Diego Martinez]

Thank u people for the help <3