Defining function handles in MATLAB

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Richard
Richard 2012-1-8
评论： Voss 2023-2-4
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.
  2 个评论
Leia Sofia Mendez
Leia Sofia Mendez 2017-7-26
编辑：Walter Roberson 2017-7-26
This was the code I was trying to write:
a= 0.0009
a= convtime([1],'samples','seconds')
This code gave an error saying that my function (convtime) was undefined. How you define a function in MATLAB?
Walter Roberson
Walter Roberson 2017-7-26
Leia Sofia Mendez:
convtime appears to be from the File Exchange https://www.mathworks.com/matlabcentral/fileexchange/28204-time---rate-unit-conversion-function .
You should go to that link, and click the download button, and download the .zip file. You should unzip to a directory that is not under your MATLAB installation directory. You would then use pathtool in MATLAB to add that directory to your MATLAB path.

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采纳的回答

Chandra Kurniawan
编辑：MathWorks Support Team 2019-5-22
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.
  5 个评论
显示 3更早的评论
Piyush Gade
Piyush Gade 2022-2-4
Whatever this is, this doesn't work.
Mark Jackson
Mark Jackson 2022-10-11
I recommend clicking 'Getting Started.'

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更多回答（6 个）

Walter Roberson
Walter Roberson 2012-1-8
Function handle version:
f = @(x) 2*x^3+7*x^2+x;
Then f is already the function handle, and you can call f(3.7) (for example)
There is no need to use feval() for this, but you could.
  1 个评论
Salaheddin Hosseinzadeh
Salaheddin Hosseinzadeh 2014-3-13
I rather this anonymous way of defining a function! It's way easier. I also know another way of doing this, surprisingly nobudy mentioned that so far! lol I'm gonna put it in the answers.

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Junaid
Junaid 2012-1-8
Dear Richard,
To define a function in matlab you can do following syntax of given function:
function n = F(x)
n= 2*x^3+7*x^2+x;
that is it. You can put end at the end of function. But it is also acceptable not to put to various matlab versions. If you put end for one function then you have to put for all function in single m file.
then you can generate random numbers, either integer or double, and can get the values of this function.
cyril
cyril 2014-3-21
编辑：cyril 2014-3-21
> f = @(x) 2*x^3+7*x^2+x;
> f(0)
0
surprising no one mentioned anonymous functions...
  1 个评论
Salaheddin Hosseinzadeh
Salaheddin Hosseinzadeh 2014-3-21
@ Cyril
Walter did, just make sure you checked the other answers and comments!

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samy youssef
samy youssef 2015-3-11
编辑：Walter Roberson 2016-9-26
here is a function i developed to calculate the log of any number with different base:
function d =log_for_diff_base(myNumber,myBase)
x=log(myNumber);
y=log(myBase);
d=x/y;
end
Nikitha Challa
Nikitha Challa 2016-9-26
x = x + a/x 2 in matlab code
  2 个评论
John D'Errico
John D'Errico 2016-9-26
编辑：John D'Errico 2016-9-26
Not a function at all. This is not even valid MATLAB code as written.
Walter Roberson
Walter Roberson 2016-9-26
That does not appear to be a question, and it is not an Answer to what was asked here?
If the question is to solve the equation
x == x + a/(x^2)
then for finite a values, the solutions are -inf and +inf as a/(x^2) would be 0 for those values, leading to the equality -inf == -inf and +inf == +inf

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Karima Benkhlil
Karima Benkhlil 2023-2-4
f(x) = exp(x^2 ) (x3+4x+1) how to define it

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