It says "too many output arguments" when I try to run the function. Why?

The function has worked great till I added the xm and ym output arguments (and the "if" structure). Why does this occur now?

function [glongitude, date, longitude, latitude, gpt, xm, ym] = GroundTrack(VettXs, ...
    VettYs, VettZs, omegarot, dt, Nt, RT)
[longitude, latitude, ~] = cart2sph(VettXs, VettYs, VettZs);
longitude = longitude(:);                        % expressed in radians
latitude = latitude(:);
tom = evalin('base', 'tom');                     % identifies the type of map
alphadate = evalin('base', 'alphadate');
d = evalin('base', 'd'); ds = string(d);
date = strings(Nt);                        
gpt = nan(Nt, 3);                          
date(1) = ds; date(2) = date(1);               

% Till the "MOLLWEIDE PROJECTION" section a simple conversion from cartesian
% coordinates to polar coordinates is implemented. This conversion is
% then used to obtain longitude (glongitude) and latitude of the projection on Earth of
% the satellite's position. From longitude and latitude is then possible to
% get all the coordinates of the ground track on other maps obtained with
% other cartographical projections.

modulus = sqrt(VettXs(2)^2 + VettYs(2)^2 + VettZs(2)^2);
gpt(1, :) = 0;
gpt(2, 1) = VettXs(2)*RT/modulus; gpt(2, 2) = VettYs(2)*RT/modulus; 
gpt(2, 3) = VettZs(2)*RT/modulus; 
it = seconds(dt);
glongitude = nan(Nt, 1); 
glongitude(1) = 0;
glongitude(2) = longitude(2) - alphadate;
n = glongitude(2)/(2*pi);                       % number of complete turns
if (n - floor(n)) <= 0.5                        
    glongitude(2) = 2*pi*(n - floor(n));
    glongitude(2) = glongitude(2)*180/pi;
else
    glongitude(2) = -2*pi*(1 - (n - floor(n)));
    glongitude(2) = glongitude(2)*180/pi;
end
for i = 3 : Nt
    beta = omegarot*dt*(i-2);
    glongitude(i) = longitude(i) - beta - alphadate;
    n = glongitude(i)/(2*pi);
    d = d + it; ds = string(d); date(i) = ds;
if (n - floor(n)) <= 0.5                         
    glongitude(i) = 2*pi*(n - floor(n));
    glongitude(i) = glongitude(i)*180/pi;
else
    glongitude(i) = -2*pi*(1 - (n - floor(n)));
    glongitude(i) = glongitude(i)*180/pi;
end
    modulus = sqrt(VettXs(i)^2 + VettYs(i)^2 + VettZs(i)^2);
    gpt(i, 1) = VettXs(i)*RT/modulus;
    gpt(i, 2) = VettYs(i)*RT/modulus;
    gpt(i, 3) = VettZs(i)*RT/modulus;
end

% MOLLWEIDE PROJECTION

if (tom == 2)
    teta = nan(length(latitude), 1);
    xm = nan(length(longitude), 1);
    ym = nan(length(latitude), 1);
    % Iterative cycle
    for i = 1 : Nt
        % First step
        tetaf = latitude(i);
        dtetaf = -(tetaf + sin(tetaf) - pi*sin(latitude(2)))/(1 + cos(tetaf));
        % Other steps
        while abs(dtetaf) >= 1e-6
            dtetaf = -(tetaf+sin(tetaf)-pi*sin(latitude(i)))/(1+cos(tetaf));
            tetaf = tetaf + dtetaf;
        end
        teta(i) = tetaf/2;
        xm(i) = (RT*2*sqrt(2)/pi)*(glongitude(i)-glongitude(2))*cos(teta(i));
        ym(i) = RT*sqrt(2)*sin(teta(i));
    end
end
end

[madhan ravi]

Beware xm and ym are assigned if and only if tom == 2

[Riccardo Basile]

Yes, infact I suppressed them when tom = 1. It gives this error also if tom = 2.

Answer 1

[Stephan]

Hi,

if you change the number of output arguments of a function, make sure to that the number of output arguments in your function call is equal or less then the number of output arguments defined in your function. Otherwise you get this error.

Consider this example function:

function [a, b] = fun(f1, f2)
    a = f1+f2;
    b = f1*f2;
end

If you put it in a script and call it with 1,2 and 3 output arguments:

% This works properly
a1 = fun(2,3)

a1 =

     5

% This also works
[a2, b2] = fun(2,3)

a2 =

     5


b2 =

     6

% This will give an error:
[a3, b3, c3] = fun(2,3)

Error using test>fun
Too many output arguments.

Error in test (line 8)
[a3, b3, c3] = fun(2,3)

Best regards

Stephan

[Riccardo Basile]

Thanks for the anwer Stephan! The thing of my case I don't understand is why this error occurs even if all the output arguments are defined in the function. I haven't tried yet but I think the problem is that "if" structure (meanwhile I've simply created another function also because this function was becoming too cluttered).

[Stephan]

we would need to see how you call the function. also you should include an else statement and give values to xm and ym in every case. perhaps set them to NaN or zero or -1, depending on what is useful in your context.

[Riccardo Basile]

So I found out that when I called this function I accidentally put an additional output argument that was actually an input... Sorry, the function works as it is.

[Stephan]

?

[Guillaume]

@Riccardo, either accept Stephan's answer, or create your own answer detailing the solution and accept it. This is so people see it's been answered and don't need to look at it anymore.

[Kumar Yashasvi]

Thank you, your answer helped me in my college assignment. @Stephan