Calling a function with no arguments

Hi All,

In my program , I'm trying to call a function with some input arguments but no outputs as I'm using this function for the purpose of plotting.

How should its syntax look like?

[ ] = function_name( var1,var2,var3) // This line is giving me erorr : Assigning an output to an empty array is not supported.

Please suggest me a way to handle this error.

Thanks in advance!

[Rik]

If you're using a function to plot, you can return the handles to the graphics object, just like the plot function does.

[John Wolter]

The title of this question could be clearer. The function has input arguments but no output arguments. It's a good question, just not the one I was searching for.

[Torsten]

@John Wolter

So you searched for:

[a b c] = fun()

a = 1

b = 2

c = 3

function [a b c] = fun()
  a = 1;
  b = 2;
  c = 3;
end

?

[John Wolter]

More or less, yes. My issue is that I am trying to code in Matlab with a head full of Python knowledge. Simple questions like, "If I have no input arguments, do I need the parentheses after the function?" often have different answers in Matlab.

I'm going to edit my comment because technically a function output is considered an "output argument" in Matlab, another difference from Python. :-)

Answer 1

[Steven Lord]

Outputs but no inputs

To call a function with outputs but no inputs, you can omit the parentheses or just include the parentheses with nothing inside them. If you were calling a function handle with outputs but no inputs, you would need to include the parentheses with nothing inside them. Otherwise MATLAB thinks you're trying to assign that variable to one or more variables and that may not work.

P = pi % one output, zero inputs to the pi function

P = 3.1416

P = pi() % one output, zero inputs

P = 3.1416

f = @pi;
P = f() % This works

P = 3.1416

P = f % P is not the value of pi but the function handle itself

P = function_handle with value:
    @pi

try % Need to try/catch so I can run more code later in this answer
    f = @computer;
    [computerType, maxArraySize] = f % This does not work
catch ME
    fprintf("This call threw error '%s'.\n", ME.message)
end

This call threw error 'Insufficient number of outputs from right hand side of equal sign to satisfy assignment.'.

Inputs but no outputs

To call a function with inputs but no outputs, just don't specify the square brackets and the equals sign.

help('pi') % zero outputs, one input to the help function

 PI     3.1415926535897....
    PI = 4*atan(1) = imag(log(-1)) = 3.1415926535897....

    Documentation for pi
       doc pi

Neither inputs nor outputs

To call a function with neither inputs nor outputs, just type its name. Or you could use the empty parentheses if necessary. Some functions may assign to ans while others will not.

clear all
whos % No variables in the workspace
pi % zero outputs, zero inputs, assigns to ans

ans = 3.1416

whos % The pi call added ans to the workspace

  Name      Size            Bytes  Class     Attributes

  ans       1x1                 8  double              

clear ans % ans no longer exists
why() % zero outputs, zero inputs, displays but does not assign to ans

Penny suggested it.

whos % And nothing shows up

Answer 2

[Mario Malic]

You can achieve it this way.

function function_name( var1,var2,var3)

However, imagine a situation where you'd like to edit something on the plot that you've made, then you'd have to find the handles of it which is not a problem if you have only one figure/axes, but for multiples, you could return a figure handle.

function hFigure = function_name( var1,var2,var3)
    hFigure = figure(1); % if you're using it
    plot(hFigure, x, y);
end

[Stephen23]

@Mario Malic: are you sure about that function definition syntax? The syntax given in the documentation is:

function hFigure = function_name(var1,var2,var3)

[Mario Malic]

I haven't had my first coffee yet! I edited the answer, thanks Stephen.