MATLAB Answers


Defining functions

Asked by Richard
on 8 Jan 2012
Latest activity Edited by samy youssef
on 11 Mar 2015

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.





6 Answers

Answer by Chandra Kurniawan
on 8 Jan 2012
 Accepted answer

Hi, Richard.

First, you need to create a new m-file then type this code

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

Save with filename 'f.m'

Then create a new m-file and type this code

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

randi will generate random number


Chandra Kurniawan
on 8 Jan 2012

to evaluate this function just type :
y = feval(@f,x)

on 8 Jan 2012

Thanks, Chandra! :)

The problem or lets say the dificulty of this code is that this couple of lines should be saved as a function and I personally don't wanna do that for a simple function like this! or even complicated ones!

Not my favorite way of defining a function

Answer by Junaid
on 8 Jan 2012

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.

  1 Comment

on 8 Jan 2012

Thanks, Junaid! :)

Answer by Walter Roberson
on 8 Jan 2012

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 Comment

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.

Answer by cyril
on 21 Mar 2014
Edited by cyril
on 21 Mar 2014
> f = @(x) 2*x^3+7*x^2+x;
> f(0)

surprising no one mentioned anonymous functions...

  1 Comment

@ Cyril

Walter did, just make sure you checked the other answers and comments!

Answer by Pratik Bhattarai on 7 May 2014

i want to solve this function M*D^(X)|+C*D(x)+K*X=F(T); to get response X(T). for any value of m c k & ft....


Answer by samy youssef
on 11 Mar 2015
Edited by samy youssef
on 11 Mar 2015
if true
  % code

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


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