# Function, input number, return a value

652 views (last 30 days)
Eric on 29 Apr 2015
Commented: Eric on 29 Apr 2015
QUESTION:
Write a small function which takes as inputs; a number a and a function g(x), and returns (a, g(a)). Note that printing is not the same as returning a value. Use the function g(x) = 2x 2 and a = 4 to test your function.
So my function right now looks like this.
function [a g(x)] = mysmallfunction(x)
a = x;
g(x) = 2*x.^2;
end
And I'm calling it like this:
clear;
[a g(x)] = mysmallfunction(4)
I get the error "Undefined function or variable 'mysmallfunction'."
But also I'm using a specific equation in 2x^2. How do I make it work for any equation.

Guillaume on 29 Apr 2015
Edited: Guillaume on 29 Apr 2015
Your tutor must have taught you about function handles for you to solve this problem.
As per the question, the function you have to write takes two inputs, a number and a function (see function handles) and returns two outputs, the original number and another number. Therefore you must have two variable names before the = in your function declaration and two variable names in the brackets of your function declaration.
Note that g(x) is not a valid variable name.
To get you started, the following declaration would work:
function [a, ga] = mysmallfunction(x, g)
Guillaume on 29 Apr 2015
No, you do not include the declaration of the function handle inside your own function, the function handle is one of the argument you pass to your function. That is, to test your function you would call it with
[a, ga] = mysmallfunction(4, @(x) 2*x^2);
Or to be more explicit:
g = @(x) 2*x^2
[a, ga] = mysmallfunction(4, g);
You only need to work out how to use the function handle inside your own function. I've shown you how in my previous comment.
Eric on 29 Apr 2015
Aha! Thankyou I finally pieced all your hints together! Appreciate it

Pratik Bajaria on 29 Apr 2015
Hello,
You just have to change a few things and it must work. Atleast it does for me. ;-) you need not write g(x) literally.
function [a g] = mysmallfunction(x)
a = x;
g = 2*x.^2;
end
Call it like this:
clear;
[a g] = mysmallfunction(4)
Check and let me know if it works for you. I assume, i have got your problem right.
Regards, Pratik
Guillaume on 29 Apr 2015
I don't think you've got it right. The question clearly states that the function has two inputs.
Guillaume on 29 Apr 2015
Eric's comment moved here:
Yes there is two inputs.
Pratik your solution would work for a defined equation.