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How to get multiple outputs from a function?

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Jongwu Kim
Jongwu Kim on 10 Jan 2020
Commented: Jongwu Kim on 12 Jan 2020
Hi, I'm using the latest version of MATLAB and trying to get 2 mulitple outputs from the simple function below.
function [x,y] = subfuntest(a,b)
x = a - b; y = a + b;
end
After I save it to an m-file, I typed subfuntest(1,2) in the command window and it only shows -1, which is the outcome of x.
How can I get both x and y, instead of just get x?

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Accepted Answer

John D'Errico
John D'Errico on 10 Jan 2020
Edited: John D'Errico on 10 Jan 2020
[x,y] = subfuntest(a,b);
When you call it with no arguments, it returns only the first, putting it in the default variable name of ans, then dumping the other arguments into the bit bucket.

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Jongwu Kim
Jongwu Kim on 10 Jan 2020
Thx for your answer but I can't get it:( I googled for the problem before I left this question here, and I found this: https://www.mathworks.com/matlabcentral/answers/14116-multiple-function-outputs
I think the accepted answer of the link is saying similar words like yours. Would you plz show any specfic function code example?
John D'Errico
John D'Errico on 10 Jan 2020
I DID SHOW IT!!!!!!!!!! I DID GIVE YOU CODE.
When you use ANY function in MATLAB, if you just use it with no output arguments, what does it do??? READ WHAT I SAID.
x = 1:3;
>> mean(x)
ans =
2
>> max(x)
ans =
3
Both calls dumped the answer to the command line, and called it ans. Do you see that? There will now be a variable in your workspace called ans.
Usually, when you use function, you put the result into some variable, named what you want.
fred = max(x)
fred =
3
>> whos
Name Size Bytes Class Attributes
ans 1x1 8 double
fred 1x1 8 double
x 1x3 24 double
As you can see, ans is still there, but now we have fred too.
However, if you read the help for max, you will find that it has TWO outputs that it can return. When you want to see the other outputs of a function, you must assign them to some variable name of your choice. (You can also call them exactly what they are in the documentation for the function, or when you created the function itself.)
[fred, barney] = max(x)
fred =
3
barney =
3
whos
Name Size Bytes Class Attributes
ans 1x1 8 double
barney 1x1 8 double
fred 1x1 8 double
x 1x3 24 double
Do you see that, now a new variable exists in your workspace called barney?
If you do not do that, then the second and later returns from a function are just dumped into the bit bucket, as I said.
Now, how should you call your function to get the other arguments? READ WHAT I SHOWED IN MY ANSWER!
[x,y] = subfuntest(a,b);
Variables named x and y will now be returned to your workspace. Or fred, barney, wilma and pebbles, if you name them that.
I would strongly suggest that you need to read the basic getting started documentatino, where you would learn these things. In fact, the getting started docs will have lots of examples.
Jongwu Kim
Jongwu Kim on 12 Jan 2020
Oh I'm sorry for you to write the long, detailed example. Thx to you, I could understand it finally:)

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More Answers (1)

Steven Lord
Steven Lord on 10 Jan 2020
Retrieving two outputs from a function requires two steps.
  1. Define the function to return two outputs
  2. Call the function with two outputs
You've performed the first of those steps. Your function definition states that it returns two outputs, the contents of the variables x and y created inside your function.
function [x,y] = subfuntest(a,b)
Now you (or really the user of your code, which could be you or could be someone with whom you share the code) need to perform the second step: call the function with two outputs.
[abra, cadabra] = subfuntest(1, 2)
Calling it with one output would only get the first input (unless the function author took specific steps to make it behave otherwise. But that's a little more of an advanced maneuver. You didn't take those steps in your code.)
hocuspocus = subfuntest(1, 2) % hocuspocus has the same contents as abra
Calling it with zero outputs is like calling it with one output that is named ans.
subfuntest(1, 2) % ans has the same contents as abra and hocuspocus

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Jongwu Kim
Jongwu Kim on 12 Jan 2020
I'm grateful to your effort too:D

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