MATLAB: Defining function handles in MATLAB

functionlive scriptMATLAB

How might I define a function handle?

For example, I want to define a function f(x)=2*x^3+7*x^2+x

I want MATLAB to evaluate f(x) at random values x. I have heard of feval and fhandles, but I don't know how to do it.

Thanks.

Best Answer

Hi, Richard.

To evaluate f(x) at different values of x, you can create an .m file and write this code:

function y = f(x)
y = 2 * (x^3) + 7 * (x^2) + x;

If you save the file under the name 'f.m', you can run the function by typing this code in the Command Window or a separate .m file.

x =  randi(7);
y = f(x)

The randi function above generates a 1-by-5 row vector of random integers between 1 and 10. The values returned by f are stored in a 1-by-5 row vector y.

For more information about creating functions, see:

http://www.mathworks.com/help/matlab/matlab_prog/create-functions-in-files.html.

You can create a handle to the function f with an @ sign. For example, create a handle named myHandle as follows:

myHandle = @f;

Now you can run f indirectly by using its handle.

y = myHandle(x)

For more information about function handles, see:

https://www.mathworks.com/help/matlab/matlab_prog/creating-a-function-handle.html.

Related Solutions

MATLAB: Do vector fields mapping R^2 to R^2 have to be coded in separate function files, or can I define anonymous functions for them directly in the script file

Can MATLAB anonymous function return two outputs?

Yes, for example

>> f = @(x) deal(x, x^2);
>> [a, b] = f(2)
a =
     2
b =
     4

But then you will always need to call it with two output arguments. The following will not work

>> a = f(3)
Error using deal (line 37)
The number of outputs should match the number of inputs.

So it is better to write a function in seperate file to handle such cases.

"anonymous function can only have one "executable" statement"

It means that you cannot do something like the following in an anonymous function

f = @(x) y=1, x+y; % not allowed

f = @(x) if x=1, y=2, end; % not allowed

"if the function file name is "nonlinear_equations", then in the script file, I store a variable f = @nonlinear_equations, and then use f instead."

Yes, you can directly use nonlinear_equations instead of f; there will be no difference. However, it is not entirely useless. For example, instead of nonlinear_equations, you need to use some other function. In the current code, you will only need to change the line: f = @new_function; however, in the other case, you will need to change it everywhere.

MATLAB: Error while fitting: X, Y and WEIGHTS cannot have Inf values.

Can you verify that you are excluding all 'Inf' y-data with your restriction on x values?

The exclude option works when using a simple case:

% Test data
x = 1:10;
y = [1 2 3 4 5 Inf Inf Inf Inf Inf]

When including all the y data, MATLAB throws the error:

'X, Y and WEIGHTS cannot have Inf values.'

[curve2,gof2] = fit(x',y','poly1')

However, when excluding all values of x greater than 5 (which covers all the Inf values for y), the fit function completes.

[curve2,gof2] = fit(x',y','poly1','Exclude',x > 5)

Best Answer

Related Solutions

MATLAB: Do vector fields mapping R^2 to R^2 have to be coded in separate function files, or can I define anonymous functions for them directly in the script file

MATLAB: Error while fitting: X, Y and WEIGHTS cannot have Inf values.

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